Catch Mawile if you can

I just did this quest and am wondering how my experience compares to others. I hit it with 1 move from my lvl 100 Greninja, threw a single great ball at it and caught it. Then they said something like “only can be caught by strong trainers”

Is it because I beat it with such a strong pokemon, or did I just get lucky on the catch rate?

Was it easy for everyone, or what’s up with this quest. Only basic walkthroughs online, nothing about difficulty or anything