Here we have T doing something motherly and age-inappropriate for OP. In fact, OP's mother also did such things for her at age-inappropriate times.

Yet what happened here was not a simple reenactment of childhood: Then, these acts were not done in affection. Here, it was. Here, it is different. This was a corrective emotional experience.

In a corrective emotional experience, a situation that occurred in the past recurs, but the emotional conclusion is different, and healing.

Compare:

If I am lonely, I might revel in friendly interaction, so different from what I might have experienced in the past, with my T. The T is not, in fact, my friend, but the friendly interaction helps me heal. I leave therapy better able to find my own friends.

Similarly, OP might revel in the motherly act of her T, so different from what she experienced growing up. The motherly interaction can help her heal. It can help her leave therapy, not with a new mother, but with the stronger self that appropriate mothering can create.

This T needs to be careful that OP does not think of T as literally her mother, just as my T needs to be sure that I do not think of her as literally my friend. To my mind, though, today's single, spontaneous act of kindness was skillfully done.