After some more research, the group that committed this is called "Indecline". They are an activist group that normally commits acts of vandalism with political aspirations, which surprises me since in this case they painted a train to look like a cat.
Their website
This organization is much bigger than I thought, making me think that UP might not catch these people. They have committed some serious acts of vandalism, so I am sure they have dealt with law enforcement confrontations before, and made sure that they can't be traced via computers. This group seems like "Anonymous", the hacking group that was relevant around 2015.
I will keep you all update with any more findings.
