No you wont get banned for the game counting private match kills toward your k/d. If you would like it to be fair do a private match with bots only, on insane. That should take away any of your guilt for being cheap.
I don't care about my K/D or anyone else's; I just noticed it after playing a few games. I just know that some people do care and that those people who care will complain. I don't want to get banned because me and my friends like to play private games to
warm up before an online match.
I realized what I was looking at. While in a private lobby you see your K/D for all Private games you have played, while in a public lobby you see your K/D for a public games you have played. The only reason I realized this was because my K/Ds were slightly
different. So I have no worries now.