The video doesn’t specify what move you should have for the German version, unfortunately. However, I could be wrong on this, but the video description does seem to suggest that the fourth slot is only important if you’re doing double corruption, which your case shouldn’t need. It’s possible that you’re just getting unlucky, since a bit of RNG is involved with the corruption.
As for the EVs, having the wrong EVs could have varying results, I’m honestly not sure. If your HP EVs are slightly off, then as long as you have less than 252 EVs, you shouldn’t have any problems; you’ll just get a Pokémon other than Lugia. If your Atk EVs are off, then you could get some weird results, since you’ll end up with a glitch Pokémon. I wouldn’t imagine that this would have much of an effect on the corruption itself, though, and realistically, the worst a glitch Pokémon might do to your game is freeze it, in which case just turn it off and it should be fine.