The mistake should have been recognized when the user previewed their post (or looked at it afterward). If you're worried about "haste" and are posting too quickly/too much to even give it a look-over then you're also spamming. The punishment is warranted.
Surely, we don't post on the forum without looking over what we type, right?
Of course, I fully agree that he made a mistake and that everyone should look and check the message before sending.
But the punishment is high jump. I'm not a moderator, but I think that the punishment in the form of a fine (by cryptocurrency) will be fair.
That is my opinion. Thank you.