You're not wrong, Poke, but a decent project manager should be able to make forecasts like that. You know that great big airport building I've been working on (you know, this one:
http://coasterforce.com/forums/threads/what-is-your-profession.39008/#post-928253) that makes FLY look like :emoji_zipper_mouth:ing tiny-town? The army of project managers on that have been making forecasts like that for over a decade on that project and are constantly reviewing progress.
Still going to argue here, if only for the sake of arguing. In terms of construction projects, FLY
is practically tiny-town, so it doesn't quite have the same level of project management behind it. You need an army of project managers to get an airport going (I daresay the Germans have learned that lesson all too well...), but a coaster project at an amusement park doesn't have quite so many actors or quite so much money in it. The stakes are lower, so there isn't the same pressure of coordinating every process to account for every bit of uncertainty. It's not a disaster for the park, or its sub-contractors, if the schedule slips a bit. If the same happens on an airport, you've got bills running into the millions pretty much immediately, because you've got sixty thousand people standing with their hands in their pockets, racking up overtime.
It seems like FLY is a pretty advanced contraption to build too, for a theme park - basically, they are building both the coaster and the surrounding buildings at the same time, inside a pit. That's more advanced than most coaster projects I can think of, so there isn't much experience to get from previous projects. Such an intertwined structure requires some unusual construction methods, so it may very well be that they've chosen to approach the uncertainty by putting in a lot of leeway on the time schedule. There seems to be only one contractor responsible for both erecting the coaster and the concrete work, plus putting large theming elements into place. The park will probably have the capability to do (or at least, coordinate) most of the rest of the work in-house. That contractor's schedule might be very generous with the allotted time, just in case something unforeseen puts everything back a week or two, and the in-house work may not be completely scheduled yet - with all the implications that has for the uncertainty of the opening date.
Of course, it's wasteful to hire cranes for longer than you might need them, or pay the contractor for hours he won't be working, but it may very well be cheaper than hiring that army of project managers and trying to map every risk in advance. They might have given the main contractor 13 months to finish while he might be done in 11, and then decided that other actors (carpenters, painters, marketing, coaster testing, etc.) will only have their schedule be determined in month 12, and be initiated on the first day of month 14. Within those 13 months, it's all up to the contractor to organize deliveries and coordinating work shifts and all that jazz. Major headache if he slips beyond those 13 months and his schedule starts conflicting with the other sub-processes, but major profit if he manages to do it in less time. It's expensive for the park, sure, but possibly less so than running a tight schedule and then missing a few deadlines. Then they'd be paying for both the rigid planning and for the delays.
This would mean that Brian's mate could get the impression that they've got all the time in the world. If there haven't been any bumps in the construction process, and the best-case scenario is playing out smoothly, it certainly makes the project manager a lot less stressed, which impacts the atmosphere on site. Sure, the contractor is still under pressure to finish as quickly as he can (the sooner, the higher the profit), but the deadline is not looming over them. They'd be given a lenient PC date, and if they appear to manage to meet it with plenty of margin, it may seem as if they don't need to stress at all.
TL;DR: the conjecture is that this is a project with many uncertainties, this is dealt with by putting wide margins in the schedule, and now everything is going smoother than anticipated. Add a few layers of "telephone" between the project manager and Brian, plus possibly a language barrier, and it's possible to see why he posted what he did. Taken at face value, the statement "they don't have a date" may be ridiculous, but I can imagine a few good reasons why he might have got that impression.