Not surprised, and it's fairly obvious if you think about the man for a second.
Trump has to be the one in charge. People never quit on him, they get fired (came up a couple of times even during the primary races, but he's got long history of it). So Trump is peeing on the fence posts here, establishing that yes, he could fire Comey and has every reason to.
However, Comey is looking into the Russia thing. Now, I don't believe (NOTE!!! OPINION!!!) in the slightest that Trump himself colluded with the Russians or directed collusion with the Russians over the election. No evidence for it, at least. But, a fair number of his staff and boosters do have Russia connections, from what we've seen. Maybe they're harmless, maybe they're not, we don't know.
If some on his staff - say Manafort, for example - were taking Russian direction, Trump is going to want to know about it, for revenge purposes. Trump plays people. He never gets played. Quickest way for him to find out is to let Comey do his thing.
Therefore: establish dominance over Comey, but let Comey continue working.
Thoughts?