Goalkeeper isn't mandatory at all. If striker is ahead of all the 10 players other than Goalkeeper when he got the ball passed, it will be offside. This one doesn't look like that at all.
It was ruled out offside by the game itself, the game developer (in this case EA Sports) obviously doesn't know shit about football then...
AFAIK, all these cyber-football matches that bookies offer are pre-recorded. I wouldn't bet on these even if they give me free money/credits.
The problem is that this position is offside in unnatural ways. Without intervention, such a position is not to be offside. There are a lot of topic here regarding the voiding of table tennis bets. WHY? A fair platform... According to what? Your platform does fair things when it's only for their own benefit.