cloud.disroot.org redirects me to my email rather than nextcloud?
Nope. Works here ok. I checked two different public IPs and browsers.
do you mean it redirects you to email app or mail.disroot.org?
thats because you probably moved mail app as the first one. Please go to settings > additional settings and scroll to the bottom where you can change the app order. First app becomes the default one loaded when you login.