I think we can safely say Kyrie was not the only problem last year. There are some growing pain/maturation issues throughout the roster that still need to be worked out, one way or another.
And this might start with Smart. He has shown to be over emotional and immature quite a bit in his career, both on and off the court.
When Smart plays, well, smart, he is a godsend. But, way too often he doesn't play smart. He tries to be way more than he is on offense. Early in the clock 25-30 footers, lazy sloppy or way too cute passes, missing the clearly open man to explore his own drives, and overtrying to pick up fouls to go to the line are not uncommon for him. These things are especially true when he is on the court with players like Tatum, Brown, Kemba and Hayward who's offense should be the priority, not the worst offensive player in the 5 man unit.
If people were calling out Smart yesterday, he deserved it. Yeah, so did Tatum and others, but when Smart was freezing out Brown(the lack of touches for Brown in this series is disturbing), taking terrible 3 pointers early in the clock(at least 2 -3 that I remember), driving wildly into crowds attempting to pick up fouls causing TO's and making bad sloppy passes...he needs to be called out.
For all we know it was the coaching staff calling him out, hence his loud altercations with them, then he went into the locker room and went off because he didn't like the criticism.
People are painting Smart going off as a good thing but given all we know, my scenario is very plausible and could be Smart being immature and trying to throw blame elsewhere while Brown stuck up for the rest of the team.