There are no “random numbers”, but there is a bit of randomness.
I asked that question to Tom in another thread, and here was his reply.
So to me, this system creates two distinctions: it makes targeting much more sensible than those tricky % numbers that have made players rage because of lacking to understand their concept. It also means you cannot miss unmissable shots, because of some raw numbers and the weird application of additions and substractions to percentage numbers found in many, many games, like a farcical “You are 3 feet away, you got a 200% hit chance, -30% weapon recoil or whatever, -80% enemy dodge skill = 90% in-game hit chance”. It could be 50%/50% for that matter, it would give the player a better sense of the two extreme outcomes (killing the target, or missing it completely) that may happen.
Just like in Valkyrie Chronicles, you still can totally miss in some unlucky streak though, but I remember in that game I hardly ever blamed the game for making me miss a sniper shot, while that’s my daily raging routine in XCOM.