Previously, Nistelrooy has said that his job was only a temporary coach before Amorim took over the team, besides that he also hinted that he would stay at Manchester United as a coaching staff considering that he has been contracted as a staff so far, so likely he would still join the team under Amorim's leadership later, the two coaches have different philosophies and styles of play at the moment as you said, but isn't it pretty good if they can collaborate?
Although it might be a big challenge but if the collaboration is successful, it will produce a very dynamic strategy and difficult to predict by the opponent later.
Nistelrooy's performance so far has been quite good and from several videos that I have watched, Nistelrooy is very happy to be able to help Manchester United to continue to develop like when he was still actively playing from the euphoria every time a Manchester United player managed to score a goal.
I also noticed that he really wanted to be made permanent as head coach but Manchester United had already brought in Amorim.
Amorin, I don't know much about him and other people might feel the same way as me. If it's just looking great when handling Sporting, then the challenges in the Premier League are very different.
It could be that Nistelrooy's help could help him get Manchester United back into the title race.
Nistelrooy's words featured in Romano's tweet, could be true during their journey there.