There is no way to infer that Mueller is pissed; you're simply projecting your own immature emotions onto him. There was very definitely collusion. THAT is among the matters that Barr misled about, using Trumps well worn phases no less. There was no legal threshold met for conspiracy charges. The ONLY reason obstruction charges were not brought is because DOJ guidelines do not permit it. Impeachment hearings face no such proscription, no such obstacle, to obstruction charges finding their way into an article of impeachment.