AVC are generally required for high speed cruise to reduce vibration levels. They are generally poor for tranistory activities due to lag times. On takeoff there should be little vibratory forces coming down from the rotor between takeoff and climb out that would require an AVC. Also AVC's only handle one frequency (n/rev where n is the number of blades). These kind of aborts are generally 1/rev where something let go in the main or tail rotor.
Now if the AVC went ape-s**t which they can do would be an issue, but I do not see why that would happen as going to forward speed. It should show up in hover.
I would suggest that if they were at 150m (500') they would be already at 120KIAS and at this speed AVC is certainly in effect. Having flown a few trips completely without AVC as it is an MEL release item, I can tell you that whilst in theory it is only noticeable in the cruise, in reality it is noticeable in all phases of flight but particularly from about 70KIAS and up. The last flight I did without AVC we checked the vibe analysis at various phases and confirmed this, although you don't need a vibe analysis to tell you this as you teeth are working their way loose. The problem does not necessarily need to have been a full AVC fail. If the AVC computer had some kind of mismatch causing a temporary mismatch between demand and output, this will cause an increase. I do not know how many FG's they use there, but if they use 6 and one drops out temporarily they may not get an immediate indication.
If it was not an AVC fault they experienced and was indeed a 1R, then another common cause has been a RIPS harness working its way loose. Not a serious problem at all, but will cause an alarming increase in vibe, and this I also know from first hand, having RTB'd with such an incident. Either way my point remains the same. No point in getting all worked up until we know the cause, and I strongly suspect it will not be as serious as some would like to suppose. The fact they flew back the same day is a good indicator. The crew still did the right thing, and safety was an absolute first, but the cause was probably found to be insignificant and a non threat to safety, so they flew home - end of story.