My DGD have always stood up in the bath (I know, It's dangerous but they are very carefully monitored.
The reason for this is so they can look at themselves in the miror. They put foam allover their face and hair and body and pretend to look like monsters, clowns etc.
They also look in the mirror whilst they are brushing their teeth. Having competions and snapping their teeth at each other.
Your ex sounds very weird.
( probably do to after the above ).
I did read a short while ago, that this is a very good way for children to establish high self esteem and self worth.
They don't become self conscious of their bodies and don't become upset if someone points out something different about them. (e.g. redhair, freckles, the usual things that make a child slightly different.
I used to do the same thing with my DC. Always had lots of bath toys and played games at bathrime. (Yes the floor did get incredibly wet).
When my DS was about 13, he even had enough confidence and self esteem to ride his sister's pink bike to an all boys school while his was being repaired.