to be fair though that was the only message he had before he got banned and there's not much else he could do to prove anything so this is still plausible
Yeah, I have to agree. If his story is true then his one line of text is all we'd see anyway.
And while it looks a bit suspicious to crop the text that way, his story is such a minor almost-non-event that it would be completely bizarre for him to bother lying/framing the guy for it.
The guy banned him for a minor reason, and is apparently a bit of a jerk.
But OP isn't accusing him of the crime of the century, so there's not really a necessity for heaps of evidence.