Look if he questioned their defensive game then yes he's out of line. From my understanding he questioned time wasting during the game, rather you believe a team with Southampton budget is acceptable or not it doesn't change that fact that he had the right to be upset about it, as would many managers. Fans themselves generally complain about time wasting of opposing teams.
Being upset about it is fine, like I said - most managers would be. Approaching a player to basically ask why he isn't attacking his team more and that he's a good attacker (willingly doing so, knowing it's the manager's instructions - let's not be daft, Pep isn't an idiot) is inappropriate.
Also I'm not sure he directly made those comments towards him, from Redmond twitter he said Pep approached him and complemented his game, which I think we can agree on isn't wrong and then he said why he didn't attack his team like he did last season, Redmond responded he was doing what his manager asked him to (now this is open for interpretation) and he said nothing more or nothing less was said.
Two things here - I think there's more that Redmond hasn't disclosed. Call me a skeptic, but the look on Pep's face hardly showed a happy tone. That's just me wearing my tinfoil hat though. Moving on and discussing what we know - I don't think that's open for interpretation at all. As I mentioned above, Pep isn't an idiot, he knows as well as anyone that instructions come from the manager. By saying what he did it's a cheap shot to Pellegrino.
People have question his teams diving Dyche said it about Berando and Wenger on Sterling, and like Pep they had every right to be angry at those decision and even question them if they were incorrect.
Yes that's all fine and well - we know all managers are moaning, entitlted cnuts. That being said, there's a difference in talking about it in a presser after the game, to actually walking onto the pitch post match, invading a player's personal space and saying it to them personally. It's completely inappropriate. If you don't agree, that's fine but there's really no more point discussing it as there's nothing more to add. What he did wasn't appropriate and was odd and thus was discussed.