They were acting that way, because the wanted to deliberately annoy you.
If I had to guess (and that is a guess, nothing more): This was someone coming back for "revenge".
If that is the case, then however it does not prove that IRC is the target of "abuse". In fact, not only does it not prove that, but it (very likely) proves that there were non-abuse cases before, but that they were rejected. I.e. someone who previously failed the captcha, and who previously came with honest intention, was to upset to let it go, and came back for pay back.
I say "previously came with honest intention" because spammers only come back to continue their "work", they don't have (or take) the time for such games. And also in order to produce the given answers, that person must have had way more Pascal knowledge than they put on display.