He's pretty clearly intentionally staying between Keller and Sergachev because he doesn't want to pressure Keller and have him give it to a wide open Sergachev between the circles. You can see him look up around 59.7 and 59.0 seconds to see Sergachev. He probably expected Miller to come over to Keller. He didn't know Lafreniere may have been able to get to Sergachev because he was directly behind him.
Probably the wrong decision, and would have been better off pressuring Keller considering he's the best player on the team, but let's not act like he was just standing around being lazy. That's clearly not what happened. You'd think this would be an obvious thing the coaches would point out and tell him (and everyone) what they want done in this situation.