ditto what teddy bear said.
One of my requirements prior to starting toilet training is that child must have solid formed BMs. So prior to starting training if they are not, I ask parents if they will try eliminating dairy and every single time I kid you not, BMs have become solid. Usually, at least in my experience anyway, the kids with this issue drink/consume lots of dairy and at the end of the day dairy is just sugar and fat. No wonder they have the trots constantly. Additionally monitor the amount of fruit intake because this can play a part.
I would not revert back, I would however go dairy free. Make the suggestion to mum, if she says no I would still go dairy free at daycare and see if this helps. It is clearly traumatic to the child hense the behaviour.
Also start keeping track of the times of the bowel movements. The sign of a healthy colon is regularity. If the child's diet is consistent then for the most part he should be going at the same time most days. If not then it is a sure sign of some type of food intolerance, most likely culprit being dairy. If he is going at the same times then it is up to you to condition this child and place him on the toilet at roughly the same time each day. If you can not leave the room, then get a potty. A potty that has the insert makes for much easier clean up. After a while of having less traumatic experiences and positive reinforcement for his successes and mirroring of verbal requests, then you might see some improvement,