How can I explain to ppl that online sites are not rigged?

[rodders133]

Ok, since posting this, I have discussed it with a friend.
He is saying it is not rigged but it generates hands that will inevitably clash. For instance someone mentioned getting stacked holding KK when other person held J5 and made a straight. Lets say they both saw a flop with these hands and it came 234. What friend is saying is that if J5 had folded pre flop, the flop would be different.

Just out of interest as I am not entirely sure how the RNG works. Has the whole hand been randomly generated, ie Is it one set of cards which include everyones hole cards and all community cards. Or as each card is dealt, is the next one chosen at random at that precise time.?