Just out of a desire to be more educated on the subject, I'd like to understand how that could happen... In this case the 2 addresses are indeed part of the same HD wallet -- it seems highly likely they are both owned by the same person.
CoinJoin (not in this case obviously but in general).
Yes, you're welcome, shitpuppets of all kinds - I just gave you a new word to use in addition to mother/father/sibling/cousin/nephew/uncle/cat/dog/goat/investment management/telegram group.