They completely ruined his character in Last Jedi, and now we are finally seeing him do something a lot of fans wanted to see from the beginning. TRAINING HIS STUDENTS. Not him being a miserable failure like they presented him in the ST.
Either that is setting up him trying to follow the ancient Jedi dogma too strictly and failing as he indicates in TLJ, or it is out of character.
That seems to be exactly what’s happening. If Grogu chooses the beskar, it’s likely that Luke will double down on the ancient dogma too much. If Grogu chooses the lightsaber, that will also lead Luke down the dogmatic path.