The issue is being handled by the BB's. In the meantime, let me try to explain you what I think happened and why.
Sorry but I can only win or loose a game and for this reason there is a final game in the qualifier. That I did not get the final game means that I won the second game and in all the qualifier!
If you look at your matches, you can see that you won the first one (the result is in black) while you lost the second match (the result is in red). Like said above, it seems to be considered a double forfeit, so both teams in fact lost. You simply cannot argue having won a match where you didn't even bring enough players to start it, so this part makes perfect sense. Thus, the engine has counted you "1 win" AND "1 loss", it has counted "2 losses" for the other team.
Why was there no third match? The system sees it was not needed because one team already lost two matches. The engine sees that the other team has "2 losses". The code probably has a simple IF branch that handles this: if either team does not have 2 losses after 2 matches, schedule the third match.
So why I am relegate?
Obviously, I think everyone agrees that one win should suffice in this case, as the third match was never played and the other team lost both. I hope the BB's will find a way to fix this for you. It may be that it cannot be fixed at this point. If this is the case, I'm very sorry for you.
Let's now go back to the above explanation.
It seems the actual relegation is handled team by team - not by looking at the league and relegating the 4 most deserving teams. This actually makes perfect sense, because they need to consider the case where both teams in the relegation playoffs throw both matches. These teams would thus have a tie, and there would be no clear way to decide which one relegates - so both relegate. The rules should obviously state this.
So, in case of teams finishing 6th and 7th, the system again looks at the record in the relegation playoffs. For some reason, it does not consider LOSSES this time but only WINS instead. So, you keep your record of "1 win" AND "1 loss", while the other team is at "2 losses". You are both relegated as neither team has 2 wins, which are required to stay in the upper league.
The fact that your "1 win" didn't count is unfortunate and seems like a bug to me.