I have heard of this before.
The pro-Soviet Afghan army did the same when it was in its last days.
Its a desperation move I think. Make some big bangs, even if pointless militarily, in hope of demoralizing some of the opposition. Or shoot with whatever is left, if no better artillery is in range.
Wow, I'm impressed someone else had heard of that - SCUDs in Afghanistan have been forgotten. I only found out about it researching a paper I was writing on the Iran-Iraq War.
The Afghan government fired MORE SCUDs than anyone - including Iran and Iraq - have ever fired. If I recall correctly, they lobbed something like 1000+ SCUDs at the Mujahedin.
It's basically a terror weapon.