A drowner spawned inside the mushroom island

*My version is actually 1.26.31.1 but I can't find it in the affects version field.

I was just building something in my base on a Mushroom Island.

• Expected result: No hostile mobs spawn since I'm on a Mushroom Island and I'm not even near the edge.

• Actual result: I heard a Drowned hurt sound, I ran to another room and saw it. Maybe it spawned inside the glass then got out before I saw it.