Referee here. I am usually fairly sympathetic to the referees and try to understand the decisions they give in the context of the game and the incident as it happens whether for us or against.
I have also watched the highlights and we played that goal a number of times to look at all different aspects and remembering this is not a luxury the referee has at the time.
The assistant referee would be of no value in this decision as he was too far away and crowded by too many players.
In any case, I do agree that Halstead was found and charged into the net by the opponent.
This was a foul and allowed the goal to happen. The referee was in a good position to have seen this which makes the decision even more disappointing.
We have to accept decisions that go against us if they are correct and put our partisanship aside but this was a foul and a referee at that level should be getting those decisions right.