The usual argument is less about piracy as a term and more the use of the word theft, and your use of the word "taking". When we talk about physical things theft and taking mean depriving the owner of that thing.
If I have something, and you copy it, then I still have that thing.
Did you read that original comment and wonder how Sam Altman and his crew broke into the commenter's home and made off with their hard drive? Probably not and so theft was a fine word choice. It communicated exactly what they wanted to communicate.
Even if that's the case, the disagreement is in semantics. Let's take your definition of theft. There's physical theft (actually taking something) and there's digital theft (merely copying).
The point of anti-copyright advocates are that merely copying is not ethically wrong. In fact, Why Software Must Be Free made the argument that preventing people from copying is ethically wrong because it limited the spread of culture and reuse.
That is the crux of the disagreement. You may rephrase our argument as "physical theft may be bad, but digital theft is not bad, and in fact preventing digital theft is in itself bad", but the argument does not change.
Of course, there is additional disagreement in the implied moral value of the word "theft". In that case I agree with you that pro-copyright/anti-AI advocates have made their point by the usage of that word. Of course, we disagree, but... it is what it is I suppose.
From the context of the comment it was pretty clear that they were using theft as shorthand for taking without permission.