Weird Egg Glitch?

[Trainer Xverse]

Ok I just had something weird happen and I need help in it's explanation. So, I was breeding my Ditto and my good ol' Charizard. So I wait around battle some AI and come back to get the Egg. As you know it takes longer to hatch starter Eggs. So I trade with my friend for a Mew because I wanted two because I was having trouble picking a moveset so I just wanted another one to use the moveset. As soon as we finish trading, my Egg hatches. And to my surprise, I was very shocked indeed, a MEW! This is weird and I need explanation. I released the Mew because I was freaked.I have never hacked, used PowerSaves, Pokegts or anything like that. Is it because I traded a Mew right before? IDK but I need help.

[Petzbreeder]

I wonder if you can hatch a ditto with perfect IVs this way.
Someone needs to try it!

Of course, from what you said, you'd need to have someone trade you a ditto for it to work.