My guess: he's trying to earn that one Merit needed for a Jr. Member signature for bounty spam.
Wasn't aware that there are bounty campaigns in the altcoin section have such low requirements.
CAPTCHA can block fully automated bot which automatically select thread at random, obtain text from AI (such as chatGPT) and then make a reply using that text. But it's unlikely it'll stop people who copy text manually from website which provide AI service.
There probably is a small number of users who might be using such a bot, but in my opinion, as you've already mentioned, the majority will just stick to manual copy and pasting from AI services. Using a fully automated bot requires some knowledge that the majority of these spammers don't have. The manual method is far easier and more convenient.