You don't need AI for this kind of disruption. People have been making fake bomb threats for years. You just have to say it, either directly to the railway/etc. or publicly enough that somebody else will believe it and forward it to them. The difference might be of intent - if you say you planted a bomb on the bridge, you're probably committing a crime, but if you just post a piece of art without context, it's more plausibly deniable.

It's also pretty common in the UK for trains to be delayed just because some passenger accidentally left their bag on the platform. Not even any malicious intent. I was on a train that stopped in a tunnel for that reason once. They're just very vulnerable to any hint of danger.