I don't think Utd7 meant it like that. Winning the FA Cup and the Europa League while also getting top four will be a great achievement given the state of our squad (many senior players under performing and lots of injuries) and the nadir we had reached under LvG during the festive period.
But the thing is that LvG is, at least partially, responsible for the squad and our bad form when we had a run of games we should really have won. It was his choice to go into the season with Rooney as the only senior forward, it's his fault that our midfield is still unsettled and at the end of the day it's his team that can't play possession football at top level after almost two seasons with him at the helm.
It's not so much about the whole rebuilding process either. Pochettino has also been at Spurs for two seasons and he's managed to create a side that, right now, looks better than ours. Arsenal are piss poor for quite some time now and they will probably finish ahead of us... again. I won't mention Leicester because they are a one year wonder but i'll say that i really doubt Chelsea will go through the same hell as we did but they will be title contenders pretty soon.
And that's where the problem lies, United are expected to be title contenders and do well in the CL. These are the two trophies that matter the most and your season is successful if you win either of them. The domestic cups are an extra, the cherry on the top of the cake (=PL or CL). As for the Europa League, i'll just mention that i don't know of a single United fan who wasn't laughing at the scousers when they were saying they did the treble (FA & League Cup plus the UEFA Cup) in 2001.
So, now that the expectations are really low, winning those two trophies and top four will be a success. But for a club like United it's not "good enough" and it must never be that way. If LvG had seriously challenged for the title for two seasons in a row an had us still in the CL this season, then he would deserve to get more time even with no silverware to show for. I believe that's what some people are trying to say.