They screaed to stand against Leverkusen because they saw the perfect performance from this team and the performance of Leverkusen during the last season was well enough which made this team unbeaten during the games they had in the Bundesliga. However they recently lost a game because of a comeback but still, Leverkusen is scary for any team in the Bundesliga.
I think Leverkusen fans also expect to see much better performance from them because they still want to see their team win the title at the end of the season.
Been scared of Leverkusen isn't what I see, rather I see the lack of confidence in that they feel already they aren't a good matchup because of the records Leverkusen has got but loosing to Leipzig might literally reduce the threat they be posing in the bundesliga all this while because firstly it's now clear they can maintain an unbeaten record again this season so they are not actually undefeatable if only their opponents are mindful to challenge them well enough. Somehow I'm beginning to see signs that Leverkusen may not be the only strong contender for the title race, they are definitely going to have serious contenders in this season and they may likely loose the title so their fans should just keep their expectations realistic enough and they will be good.