Without wanting to sound entirely blinkered, how are you so convinced from that still image -- which accords with the moving image on SeagullsPlayer -- that it's 'just' offside. In my book, to make such a claim, you need to have an image that is in line with the players at the point the ball was played. From the still image provided, alongside the moving image I've seen, I'd say that looks level. Although if there is an image that is in line with the players, or there is a convincing explanation from that image, I'm willing to yield.
Over to you folks.
ps that 'goal' was a cracking move, and Colunga's shot was great too.