To answer whether the practice times are harmful requires that you look at whether they get adequate recovery afterwards, whether their practice times start to suffer after, whether they get injured more often as a result, and of course how the races go.
You can also explain away some of these practice pr's by rapid improvement (i.e. the shape that would produce an even bigger race pr at that time), better pacing in that controlled environment, and failure to get into a race at that distance when in that kind of shape.
I'd tend to think that you should do your workouts at an ambitious pace in order to keep improving, rather than at, say, actual 5k pr pace for 400 repeats. Substitute ideal goal pace for actual pr pace, and then run as fast as you can (with no finishing spring, of course), commensurate with finishing the workout and not being destroyed the next day.