I've had dozens of accounts where they've given me stuff that is much more rare or sought after while I give them something that isn't really an equal trade. Just got a Gurdur from a guy in Wonder Trade, Japanese of course, it evolves when it gets to me. And I just traded a Flash Fire Vulpix for it. They do this all the time and I can't even imagine what they might be thinking when they give away something decent for something common.
My first thought is they're thinking "haha stupid American, you so bad at games compared to us, I give you free things to make you feel betta so I keel you lata."
So yeah...
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Well, maybe they just want to make the wonder trade better. Gurdur isn't a legendary, and no one will keep using it if people just send in level ones all the time. They just probably wanted to be nice to some random person in the world, and hope that person follows their example