Its all random. Literally up to the RNG god to decide who comes out on top. If I could be bothered, I'd find a 1v1 IS-2 vs. Tiger duel I had the other day in my stream VODs. It wasn't as controlled though, I was continuously reversing my IS-2, always showing my front, so this affected accuracy on both sides but they were both engaged the whole time (never out of los, no range issue etc.). My IS-2 eventually won. Its literally how lucky you get. Its just as possible the tiger may have got 3 or 4 crits in a row and won.
No, not really.
Every single math and probability gives Tiger an easy win over IS-2.
If IS-2 wins, THAT is pure RNG luck. If Tiger wins, its just confirmation to the rule and tiger wins vast majority of time.
You've had one lucky game, that doesn't make it "all random".