If you look at the teams FCSB has beaten those are placed 34th, 30th, 19th, and 17th.
By comparison, Manchester has won against 13th, 10th, 11th and 18th.
Hard to bring this performance even close.
Sometimes, it can't be determined by the stats. If you are watching the match FCSB vs Man United now, you can see that Man United only could score goals when it is in second half of the match. There was no goal in the first half of the match. It means it is not an easy match for Man United, they are struggling to score goals. However, at least they can win the match whatever the number of goal. Also, it becomes not easy because they are playing in FCSB home. But, no doubt that Man United is very likely to win this match.