Well, it should not work. Because make faces what it does is precisely that, to make faces from edges (or to be clear from two equidistant vertices). If you select 2 groups of edges, like the example in my screenshot, Blender doesnt know what edges to join to make the faces, so you get everything joined. Thats completely logical and i understand why its happening.
And it should not work for you either. Now, it works for the guy doing the tutorial?? not a clue. As you know a lot of people who make tutorials avoids and ignores a lot of steps in the process (and the guy who do these tutorials do that all the time), and i assume most of em confuse “make faces” with “bridge edge loops”, two completely different things.
The only problem i was having is that i couldnt not understand why “make faces” should work in that example. It shouldnt, but it does in the tutorials i watch. My confusion is there. Now, it is fixed using bridge edge loops, but i like to learn everything i can before i ditch something out.
Now, it works for you? congratulations. But im pretty sure you cant explain why… lol.