You would be shocked how many buildings from the past which are wildly flammable. Expanding foam is highly flammable and a lot of theme parks are riddled with the stuff.I don't want this to come across as an accusation or anything, but I feel like this is further confirmation to my impression that proper fire-damage proofing was slmost non-existent before the 2000s. Looking at the pattern of damage now and from the 2018 fire, both times it appears like the affected areas consisted mostly of metal framework and expanding foam.
Generally building regulations for fire tend to not be retroactive unless major work is done. If that ride was largely left as-is for decades then legally there'd have been no requirement to upgrade the fire rating.