Except for the bottom cell group. every negative end of a cell is connected to the next positive group, right? So it doesn't matter whether you put the balance wire to a positive or a negative.
So if you connect the black wire to the first negative terninal, you could connect the next 12 wires to negative groups, but the last one #13 has to be on the last positive terminal.
In the you tube videos, they must put the black wire on the first negative terminal, Then the 13 red wires can go to the positive terminals in sequence, Easier for people who don't understand the wiring to follow. Better to understand why each wire goes where it goes, Hope this helps.
From my point of view, for your battery, I would would rather solder each balance wire like they did, in between two cells on the negative metal strips. That because there's nothing under the strip that will short circuit if I do a sloppy solder. If I move down the strip to the positive terminals and do that, there's going to be the steel negative side of the 18650 can right under the solder joint, only protected by the cardboard ring and mylar film. Screw it uo, and you have a short cirfuit I can't easily stop. Fire. Explosion. End of the line.