I think that guy probably had a bit of luck. Most times when I've played played or specced pubs there's that one guy who goes 0-40-0, there's supports who rush ags (and never get it), half the team doesn't speak english, there's all kind of people who feed like fuck and you get stomped by a stack.
Escaping low elo as a solo mid may be easy, but if you play 5 how can it be possible? I can deward every ward in the game, buy tps, dust, smoke, force 10+ kills in the laning phase, stack and pull, save the carry and mid from ganks, block the enemy jungle, gank the jungler, snipe the courier, but in the end I can't win the game no matter what I do. Even in the rare case when I mid with a non-semi-carry I can get tons of kills and assists without deaths (something like 10-0-10 during laning), win the lane with 60-30, but no matter what, bat rider isn't going to win the game.
Getting pushed outside of your pubs mmr is possible if you play with a stack, for sure.
My win rate with farmers and solo mids is generally >70%, but in pubs there is almost always 2+ players who want mid and <0 players who want to be support. I should just roll luna/drow/np/dp/bs all tell people to fuck off from mid, but I would feel like a huge asshole doing that. I guess that's why most people I know who play high mmr are egotistical assholes who just play mid ._.;