The teams are all split into groups of 4, (A, B, C and D). After that each team in the group will play every other team in the same group in a Bo2 (best of 2).
If the team gets a 2-0 win then the team gains 3 points, if they tie 1-1 then both teams get 1 point. At the end of all the matches, the top 2 teams from each group go into the playoffs where the top 2 make it to Berlin.
Now I'll explain why BOOM can qualify and X10 can't, the tie breaker rules are that if there is a tiebreaker in points then the round differences will be compared, by comparing the map where X10 won with the map that BOOM won, you cna see BOOM won 13-6 while X10 won 13-7, this means that BOOM is ahead as they won with more rounds.
TL:DR: Boom won by more rounds if you compare the games