Gastly trade?

In the second city, we have a trainer who trade a Gaslty. I wonder why ? Is-it special ? I ask this because in the road who lead in this city, there is lot of Gastly to capture. So I wonder if it’s special ? I have juste one Heatmore, so i don’t want to trade him if the Gastly is like the other Gastly that we can catch before the city.

Special in a sense of it being a traded Pokemon which gains more exp than normal. Making it an easy Pokemon to raise.

Ah ok thanks, i didn’t know that.