I don't think that Michael was 100% sure that Frankie wasn't involved somehow. He shows up unannounced and tells Frankie "I didn't want you to know I was coming". Even though he was pretty sure it was Roth I think the outburst was Michael's way of gauging Frankie.

More importantly even someone as self-contained as Michael still needed to vent sometimes and Frankie happened to be the person unfortunate enough to be around.

Lastly it is also an excellent opportunity to shame/manipulate Frankie into doing what he had been balking at doing-settle the troubles with the Rosatos.

Frankie just pawn in game of life.
lol

"When the snows fall and the white winds blow, the lone wolf dies but the pack survives."
Winter is Coming

Now this is the Law of the Jungle—as old and as true as the sky; And the wolf that shall keep it may prosper, but the wolf that shall break it must die.
As the creeper that girdles the tree-trunk, the Law runneth forward and back; For the strength of the Pack is the Wolf, and the strength of the Wolf is the Pack.