In chapter 7.3 page 4 he says that his first real conversation was him asking questions and listening to what the speaker had to say, and is depicted as between him and an imp.
This very well could be the first thing he's spoken too.
@gaigous That's the MC from the past. He was also shown at the start of chapter 1.
And the reason why he currently looks different is probably because he changed his appearance, after all Ekidona doesn't know that he was the hero.