Why would an elo booster ever tell you they're elo boosting if they're on the other team and won

Those games that you can tell, they're not just doing better, they ARE better.

Then you get out, and the dude says "sorry Zed, I'm master tier."

Then you shouldn't be as low as gold in 75 games.

"It's my friends account lol."

Why would they do that? I'm already salty about going 1/10 in my promo, why would you admit to elo boosting? I'm GOING to report you :P