it is glued at least on my E32, only clips are where the interior light is, see my website below under headliner repair.
Here you can see the clips on the E34 Touring
Roof trim-headlining moulded/handle BMW 5' E34, 525i (M50)
Usually the 3mm foam in between the headliner material and the board just disintegrated and that causes the headliner to fall down.
*DIY Headliners Replacement. - Bimmerforums - The Ultimate BMW Forum