The Wels FA are, apparently, following FIFA rules. Essentially it seems that the referee saw the challenge and deemed it to be fair and therefore the matter's closed.
Now you have to ask how he could have at least not given a free kick, but there you go. Bothroyd has been quoted thus:
Bothroyd insisted he had been the wronged party, saying: “It was me who was fouled. Their player knocked me over. Nobody should be sent off for trying to win the ball cleanly – and that’s what I did.”

As for the FAW - there are numerous examples of them treating Cardiff favourably whenever they've been up before them for crowd related issues - which is nearly as often as Millwall.
Farnley/Pudsey Leeds
40m asl