If it was a double movement then a penalty would have been awarded. I don't think it was a double movement; I'm 90% sure that under the rules a double movement requires you to lift the ball and promote it; basically making a second attempt at grounding it; Fonua's effort was all in one motion.
To answer your other question. Yes the Tigers were good and Souths were absolutely terrible. Losing Sam Burgess has just been one of our problems but its no excuse - sort of similar to the eels losing Hayne; both clubs knew that they were losing their respective players well before the season started. However, a lot of people seem to overlook the fact that we have also lost Teo, Tuqiri, Auva and Kyle Turner - all part of our premiership winning team. Add to that injuries to the likes of Glenn Stewart (who we should never have signed) and Adam Reynolds and its becomes very hard for us to compete. In saying that, that is only the tip of the iceberg..I could go on for ages we have that many problems..but that is for another thread.