Raid spawned "inside" mountain base

[nuschler22]

I've never seen that before.  I received the raid notification and the raid spawned inside the kitchen.  The area is within the base and marked "inside." 

I have an outer wall that is an embrasure, but still shows it's "inside" with different temperatures both outside an inside.  I'll have to make that it's own room and see if I get a similar results.

Anyone else had a raid spawn inside a cave base?

[Robovski]

If your roof is thin or constructed the raiders can pod in; only the thick mountain roof stops pods and mortar shells.

So the raiders go through a thin part of your roof - if that is fairly deep in you may have a grotto nearby.

[Devon_v]

Totally, drop pods can pierce anything other than "overhead mountain".

[Goldenpotatoes]

The raid message says if the raiders are dropping in or if they're coming from off the map. Was there scrap metal and stuff around where they spawned or did they just poof in?