He's basically said "I have skill set X, which I'm trained in and have been honing for years. For my company, I need skill sets X and Y. So I'll do Y and find someone else to do X."
No matter what X and Y are, that's just the wrong way to solve that problem. The key issue in this case being that he is assuming the marketing/user acquisition stuff is so easy that he can just pick it up on the fly with no prior experience.
I don't know, If I can't do Y how am I going to hire an A player at the Y game. Being good at X means I can evaluate others in skill X.
You do X, hire Y - You have one skilled person, one question mark.
You do Y, hire X - You have one unskilled person, one question mark.
Seems pretty simple to me that the first is better. I suppose that you could make the argument that Y may be easy to pick up, but if that's the case it should be all the easier to just hire someone else with a proven track record.