Maybe the processing stack goes “trigger achievements” before “trigger squish” and whoever oversaw that was like “eh, most people have this achievement already and switching the stack order would be a headache, that is not cost effective” and this was a “won’t fix” kind of bug situation.
I doubt that a blue will be able to enlighten you on the matter (even though it doesn’t hurt to ask) but I reckon that this is a solid working theory given the circumstances.
Congratulations on your early achievement! 