The Bug
Although an unconventional weapon, beds and respawn anchors can be used to hurt and kill entities like any other weapon, but yet they've been forgotten about in the advancement code. Using a bed or respawn anchor does not trigger the advancement criteria player_hurt_entity.
How to Reproduce
I've attached a simple datapack with three advancements: One with a tick criteria telling you you've successfully downloaded the datapack and it's working. Another just with a player_hurt_entity trigger without any conditions, and lastly one that's the same except it has an is_explosion condition.
You'll find that hurting entities using exploding beds and respawn anchors doesn't even trigger the second advancement.
Confirmed, mobs don't drop experience as well