Level up Monster Summer Badge with Wormhole?

Part of the description for the Wormhole ability says:

You must defeat a boss level after using Wormhole in order to level up your Monster Summer Badge.

However, I have never used a wormhole and I have only defeated around 500-1000 bosses, yet my Monster Summer Badge is level 1880. Is that part of the description really true?

That quotation means "if you use a Wormhole, you must then defeat a boss level to level up your Monster Summer Badge". In general, you level up the badge by defeating boss levels, and it's saying that using a wormhole to skip a boss level doesn't count for that purpose.