Instant Runoff Voting is essentially STV in the degenerate case of single seat constituencies rather than multi-member ones. So you're both right! It is in some

Instant Runoff Voting is essentially STV in the degenerate case of single seat constituencies rather than multi-member ones. So you're both right! It is in some sense the same system, but it plays very differently in that the results are majoritarian rather than proportional.