Yep standard pressure vessel. They only need to look at the nameplate on the side to find the registration number and it can be traced to the owner and manufacturer. All vessels over atmospheric pressure are required to be registered. Finding out who messed up would be easy.

Looks kinda like one of those big pontoon thingy's that are attached to the bottom of multi-hull boats to keep the hulls out of the water if the boat is going to sit for a while. Saves on the costs of scraping the hulls every 12 months or so. But I doubt this would be what it is because of the gasses it contained.

My "not so serious" suggestion would be its a giant sushi roller.