It just sort of took the "Marvel" part of the prompt and threw in everything and anything Marvel related (instead of just the F4). Though I guess since the MCU has its multiverse where anything and everything is possible, Deadpool with an arc reactor in the F4 could be canon.
That's actually why I was testing it originally, because it feels like you throw anything even remotely well known at any of these AI things and it shuts you down. I remember wanting to a logo for a Sherlock Holmes detective agency (a character that's long been in the public domain) and it refused to that. These AI generators are so restrictive half the time that they just refuse to do anything for you.