Lore time!

Grogu was smaller and more reserved even during the his time during the training with Luke Skywalker. After Din returns to pick him up, the two Jedi was pretty hesitant but somehow knew Din has changed a lot since the last time they met. Grogu already sensed him coming and told them beforehand. He had learned all he needed to learn at the time. And unfortunately, it was pretty obvious that Grogu was not interested in being a Jeti nor it fits his magical abilities.

After getting Grogu, Din wanted to spend some time before returning to his duty. He takes him to meet his Ba’Buir Akumu. (grandparent) Needless to say, Grogu was very happy being spoiled with lots of treats from Akumu. Akumu knew what he was as well but Grogu wasn’t sure and slowly opens up to him as well. After a while, his body started to change. Very noticeably, his scales are more iridescent and his snout is more prominent. And had a tail. All this surprised Din for what he is. It made happy to know that he is just like his Buir (parent) as well.