The last time I checked Portsmouth were in League 1.
If that were true that titbit of information would have leaked out, it always does.
No, he is not playing because Conte wanted a proven wingback as opposed to "a club signing" with potential. The only reason people like me are irritated by Conte's behaviour is not because he regularly chooses Emerson ahead of Spence, a player who regularly develops a nose bleed when he crosses the half way line and who needs Kulu to hold his hand just to make him good enough to be ordinary.
If as you say he is not Premier League ready then I would suggest starting him against Portsmouth, a Division One club, would be right thing to do.