This. In fact, it indeed is not "purely" random, it is pseudo-random, because the RNG must be based on something - it must have a "seed".
The seed in Neverwinter Nights, another Bioware game, was for example based on the area you were in (among other things), and it did reset each time you changed an area. Also, once the seed was set, the "random" sequence of numbers was always the same, meaning that if with seed A you got rolls like 45, 89, 76, 3, 15 etc., you would get exactly the same rolls if you would manage to get seed A again.
The consequence of this was that a) some areas were more "likely" to produce a successful roll, and b) changing an area after a series of unsuccessful rolls was a bad idea since the RNG had to start "from the scratch", while in the original area you would be approaching the "good numbers". I don't know what kind of RNG is used in SWTOR, but from my observations, the point b) seems to hold true here, too - when I fail RE'ing something five times in a row, I try, if possible, to make the next five attempts in the same area - so far it has paid off.
Though, of course, it may also be just a "Las Vegas casino manual".
If the seed is based on a "normal clock" certain times of days will produce the same result. But there are better ways you can even use a clock a seed and you could do some real advanced logic stuff if you really wanted to get closer to random.