It wasn't only that one moment that they thought that it wasn't their son. Alot of chapters ago they were saying how different he is, also imagine your son a drunkard who caused trouble wherever he went change into a genius who can build anything, got your county out of debt, got recognition from the ruler of your country and from almost every other species. Can't forget about him being friends with dragons and he did that almost overnight. Anyone would be suspicious, even Javier got suspicious at times before the MC told him. And they say that the clothes is something that he wanted to wear since he was a child and when they gave it to him he has almost no reaction to it,
dude how tf did they make that distinction from that single interaction. they mentioned his grandfather and lloyd, who was barely paying attention to their words, just rushes past them and agrees with whatever theyre saying. the parents immediately conclude that lloyd isnt the real lloyd and dont even take a second to doubt or directly confront lloyd? how disappointing. their faith in him was so little despite everything hes done for them