That self-effacing, almost insulting "thanks for hanging out with our screw-up, useless kid" thing is a standard Japanese trope that is at least partially based on real Japanese culture, which prizes being so excessively modest and deferential about yourself and your family that you have to act like you/your relative is a terrible, unlikeable sloth of a person who is below deserving of basic decent treatment so that nobody could ever accuse you of being boastful or arrogant (unless you or that person are legit "special" in which case that level of arrogance is considered acceptable because you've "earned" it).
This is entirely a cross-cultural bit of confusion where something that is a part of the fabric of Japanese social interactions is viewed differently by westerners because it's not how we do things and that re-frames the discussion dramatically differently.