I saw that specific match when the video released (I, shocking no one I'm sure, subscribe to that channel). There are things at both the strategic and tactical level that I'd consider failures on the Rebel player.
The 4 Thug list is the San Antonio Spurs of X-wing. Durable, reliable, not flashy, and will beat you by capitalizing on your mistakes. It was big in the meta, went away some under new hotness, but is still a solid workhorse.
But you need to have a plan to defeat it. If you improvise or freelance, you will lose. The Rebel player had a path to victory, but it was a path that was lost due to tactical failure at the initial engagement. The key to beating the Thug Life list (as it has been dubbed) with this list relies on a strong alpha strike knocking out one Y-wing quickly, while limiting shots back. The first approach works, getting a range 3 shot with only a single ship in range. However the next stage is ramming in to get at range 1 with both ships. Done right you can kill 1 Y-wing in the second round of shooting (first if you get a lucky crib through), and have a second severely damaged.
The Rey/Finn combo is the perfect tool for this, adding a die to both attack and defense is an amazing way to mitigate, but you need to keep them in arc. The failure to do that is what doomed the Rebel player.
The other failure was before it hit the table. Being a fan of both Rey and Miranda (and quite successful with both), I dislike the Miranda build. He never leverages the long range scanners to use the homing missile, which also deprives him of the Advanced Slam mod. Some point shifting and I could make a (to my mind) generally superior build. Still, even with that list as is, it was winnable. But failing to get in range 1, and failing to keep them in arc with Rey, doomed him.
Now credit the Scum player, they flew their list masterfully in the initial engagement. The Rebel player was outplayed. But play that match 10 times, and that is probably a 6-4 split with equal skill. Tweak the Rebel list only a little? 5-5, or even Rebel advantage.