Personally I wouldn't consider that abuse either. IMHO a good interview is supposed to be hard. How else can you differentiate good candidates from bad? Perhaps others disagree.
A good interview doesn't just filter out bad candidates - it also persuades good candidates, who will undoubtedly get other job offers, that they want to work for you. It shouldn't be a courtroom-style grilling - it should be difficult but fun. Honey to catch your flies instead of vinegar.
I'm not saying this was a problem with the interview described as there isn't enough detail in the original post to say what happened really.
Personally I wouldn't consider that abuse either. IMHO a good interview is supposed to be hard. How else can you differentiate good candidates from bad? Perhaps others disagree.