let's assume you did not cheat in that match.
If we just go by the facts for now: in the video you yourself admit to buying that account, you have no idea who that account belonged to or what it was being used for before you bought it. Even if it had 0 hours on deadlock, the account can be traced back to a collection of many other accounts created by the same people who would make and sell accounts for cheaters.
While valve hasn't made an outright statement about buying/trading accounts, but you can't blame them if you do stupid shit like this.
As an analogy, think of why people get a prescription for the drugs they need, instead of getting them from a shady dealer, even if its cheaper and has less red tape
If you are a legitimate user, who just happens to be puny enough to smurf, you yourself make an alt, valve hasn't made an actual statement about smurfing yet either so i doubt they would ban you immediately for just smurfing (because a large chunk of high elo would need to get reprimanded, really) unless you do other vile shit alongside it