The above comment wasn't a passage in a legal document, it's a comment on a discussion site. "IP theft" is a colloquial, non-legal term generally referring to violations to copyright law. Neither the RIAA's complaint nor the DMCA contain the word 'theft'.
Well sometimes though. In the case of the Computer Fraud and Abuse Act the word “unauthorized” can mean basically anything the DOJ wants to pull out of their asses and prosecute. Fortunately we have courts to remove ambiguity.
The idea of copying as theft isn’t new but I agree it’s not really the same.