alt Hacker NewsCTA is very obscure. As a mobile dev I refuse to call CTA as anything other than click or tap to action in which case it should be TPA. Also many folks (esp. PMs confuse CTAs with button clicks). Anyway, CTA in this context didn’t even ring a distant bell either for call or click and I am glad it didn’t.
I think in UI design it usually is intended to refer to the main thing you want/expect a user to do in any given situation, i.e. having multiple CTAs is a bit of an oxymoron while having multiple buttons is not.