This is completely incorrect. 2.52 is where the frame starts.
2.52 - The defensive shape is good, McT has not tracked the same man as AWB - he's nowhere near him - the midfield is actually doing fine, McT and Eriksen are both close enough to their runner, AWB has his runner, the issue is that Bruno does not follow the runner he sees ahead of him. I can't be too critical of Bruno because we are down to 10 and he's not a winger but the freeze frame makes this situation very clear.
2.53 - cross comes in. McT is nowhere near AWB again (I'm wondering now if you even watched this back or just expected no one to check?), McT has come too deep arguably as his runner is now on the edge of the box but every player is goal side apart from Bruno here. In this image the only player you might pass on from a defensive standpoint is Eriksen to Maguire but that's not what we're discussing.
2.55 - ball arrives at back post, now McT and AWB are near each other but it's not from tracking the same player, it's because AWB was tracking the player and he ran towards the centre of the goal. You see Bruno start to react but it's obviously too late. Varane also has to be tighter on his man there, in the 6 yard box you can't be letting a striker drop off that easily.
If you want to criticise AWB, the back pass was pretty crap but he is no way at fault for this goal. McT doesn't need to drop into the CB line, it's Bruno's man who assists (albeit we have 10 men so it's a bit harsh), it's Varane's man who scores and, really, we should have been much closer to the original cross.
If you mean it's no coincidence that a team paying against 10 does what every team playing against 10 does, no it's not a coincidence. You target the areas of the pitch which are stretched and hardest for your opponent to cover, which are the flanks.