You should also check their performance in their own domestic league in this season, both Bologna and Girona performance are terrible, while Leverkusen is still fine even though not as strong as in the last season. But, Leverkusen met easier opponents, like Milan and Feyenoord, which is nothing surprising they can won those match.
After all we still have many upcoming match, Girona is quite lucky their opponent not that strong.
I have seen Bologna and Girona playing badly unlike last season, both teams in their domestic matches had very doubtful performance while Leverkusen was very lucky that the opponents they faced were not at the level of a strong team this season.
Leverkusen has shown their best at the start of this season and the group Leverkusen will face Milan and Feyenoord in the grub phase, making it very easy for them to get points. The match has just started, let's wait for the next match.