Grimrock

On my run I somehow managed to on level 3. On replay I am not able to get it again - was it random loot?

"Intermittent" would be a better description. The skeleton archers only drop frost arrows, though they don't always do so.

So if they have it in inventory "to drop", is there any way to make them drop it? Like not let them to shoot at all?
In other words:

Lex wrote:So if they have it in inventory "to drop", is there any way to make them drop it? Like not let them to shoot at all?
In other words:

SpoilerShow

is this frost arrow first one they are using or it is just some simple % chance to drop?

I highly suspect that there's merely a % chance (or at least there's always uncertainty involved). I've killed them without them getting a shot off and didn't get a drop. Conversely, I've killed them after a fair amount of shots and gotten a drop.

Seems its useful to save the game before fight and load if no drop

I think it has to do with how quickly you kill them...as in if they get to shoot several times they might use them up. I noticed this when I was playing the first time but forgot; when I tried to kill them again and prevented them from shooting I got arrows.