It also says “free of installer bundles” while (at least in past, don’t know about now) their default windows installer was including ads (source)
P.S.: If you want to disable the in-app ads, here’s how to: https://gist.github.com/yunooooo/87564a0293a1c7a53fb3e233a604c638
JDownloader is a tool whose continued development is well worth supporting.