How do One Way Wall-bangs in CSGO work

The ban systems works as follows:

1st infraction: 30 min.
2nd infraction: 2 hours.
3rd infraction: 24 hours
4th infraction: 7 days

Any one of these infractions get reset after 7 days.

How the banning system works (To the extent of my knowledge):

1. Dealing 80/90+ damage to a teammate at start of game will be instant ban.
2. Doing 400+ of damage to teammate(s) over the period of the whole game can get you banned. (You usually get a warning telling you that you have done a lot of damage and the next time you attack a friendly you will be kicked)
3. Killing 3 teammates

How you got kicked and he didn't: He didn't get kicked purely because it wasn't at the start of the game and in spawn. When it's like that the game knows that there are enemies around and sometimes that you are likely to either accidentally attack your team mate or maybe even kill him. For this they make exceptions. However if you were to do it as a continuous burst of fire (so all his bullets hit you without any pause) then he would have gotten kicked/banned.

In cases like that all can really do is report him through the use of the scoreboard as someone has mentioned in the comments section.

There is a difference between rank and skill group. The skill group in CSGO is how you match up to other players. The rank("level") however, is essentially irrelevant, the only thing that matters about it is you have to reach Rank 3 to play competitive. The only other way competitive is linked to your rank is that it yields larger amounts of EXP due to the longer play time. Your skill group is the amount of wins and losses in the competitive playmode.