It is a ridiculous decision to suspend him at all, never mind for three weeks. Apart from the fact that it is clearly disproportionate, it simply draws attention to a referee getting it slightly wrong. As if referees don't have enough to deal with. He forgot his coin, found a way round it which didn't impact the game in any way and everyone was happy. Where is the problem?
Incidentally at a game I lined earlier this season the referee used a plain plastic disc which was a different colour on each side to toss. Since this was most certainly not a coin presumably he should also be banned.