There seems to be a fundamental disagreement between Amorim and his sporting director. It has not been made clear what that disagreement is but Amorim referenced criticism from Gary Neville and other pundits. Neville has commented on his tactics and his uses of subs. Reading between the lines, I think the disagreement relates to the playing style and tactics.
Whatever the nature of the disagreement, his statement is very strong and challenges the board to back him or sack him.
They are in the 5th spot but imo that does not reflect progress at the club but the weakness of key rivals in the league. Liverpool, Spurs, Chelsea, Newcastle are all in disarray. I think Utd will try and smooth this over because they have no alternative.