If I actually cared, I could go find 20 examples of the same thing for every single team in the league. Sometimes things work, sometimes they don't. Sometimes players make the wrong play. That's hockey. That's life. One example proves nothing.
I also don't actually know if Brown made the wrong play there, without seeing. There are multiple reasons you might pursue a puck carrier if you aren't going to crush him along the boards. Push him further into the zone to let your team change, cut off angles, be there in case the player makes a mistake or fumbles, etc. before you go off yourself. I don't really want Brown engaging physically and putting himself behind the play when he's at the end of a shift and tired. If the defensemen moved the puck up past Brown, that means Leafs have a fresh change and numbers back, so how is that the wrong move or Brown's fault?
I could also go find examples with the Leafs where they did exact same thing, and the defensemen fumbled and gave up the puck, or the Leaf player got the stick in there and got a goal, or a chance, or drew a penalty.
Maybe if random nothing plays from months ago are getting stuck in your head, then you're focusing too much on the wrong things.
People on this site have a weird obsession with hitting. I've said it before and I'll say it again. Hitting isn't always the right move.