If the company is rotating him to positions that aren't his line of work, or what he studied for then I think it's a perfectly reasonable reason - he should be

If the company is rotating him to positions that aren't his line of work, or what he studied for then I think it's a perfectly reasonable reason - he should be prepared to explain it more than "I didn't like it" - because that would be an issue, but otherwise I don't see the harm. In the end he needs to be sure that he is making the right choice in leaving and deal with the consequences if it's the wrong decision - or possibly be happier else where if it's the right decision.