Greig went down on the play for a few moments, and the rest of the players on the ice met together in a scrum. After the play had calmed down, the referees reviewed the play and gave Rielly a game misconduct for charging. It's pretty much a certainty that Rielly will hear from the Department of Player Safety for this, and will likely receive a suspension.
It's a gross act of retaliation after giving up a goal, but also, it's the expected response of prideful and highly competitive hockey players when they get taunted with a cocky, classless, and disrespectful empty net goal like Greig did. Greig knew that what he did was a show-off move, and he paid a price for it.