The only time {attack:{}} gets updated in an interaction entity is upon LeftClick (punch).

Due to the way "on attacker" works inside the /execute command, the assumed result would be anytime interaction is attacked but it only works with LeftClick.

Reproduce:

Summon a minecraft:interaction.
Use either execute on attacker or @s[nbt=\{attack:{}}] to detect when it is attacked
It will only update on punch, not on projectile

Now summon a minecraft:pig (or anything similar)
Use execute on attacker to detect when it is attacked
It will update on punch, or projectile, or any other attack on it