I'm a field engineer for a commercial property insurance company, and would have to say that if the bikes did not have gas in them the fire would have easily been controlled by sprinkler protection. With gas in the tanks, it would really be anyone's guess what would happen. What I bet happened here is that the building was on fire, not the bikes, then it got powerful enough and spread to the bikes.
Europeans are much less likely to install sprinklers in their buildings than we are, they tend to rely on preventing fires from starting. Really strange that whomever was running the museum didn't have any sprinklers. You can install sprinklers for about $1.50 / sq. ft., cheaper than some carpeting.
The other possibility is that the place had sprinklers, but a valve was shut.
I'd bet this place was insured, but not by a company that puts much of an emphasis on loss prevention. There are a few fly by night types out there that pop up when rates are high (like right now) some of them don't send out engineers to their insureds, they just roll the dice & play the odds, like auto insurance companies.