What age level and who is the "someone" saying it?
If HS, I'm with your friend and Pitchingfan... taking I/O on the field means each player at his position. The exceptions typically are some tournaments. "Do you want to take I/O?" means the normal routine with each player plus backups at their designated position, making throws to bases, etc.
I understand the error in my logic now, but do you see how I could be confused at the phrase? My assumption was that the outfield is technically "on the field" and we usually take our in/outs in the outfield. I guess I'm just trying to justify my bad logic. But do you see how someone could make that mistake?