Ah yes DBM (and other addons) that are set to alpha builds. Okay, here's what's going on: when you set the release type to Alpha as per your picture above, then files on DBM's project page (Curseforge) will show some alpha builds. That does not mean those alpha builds are going to Curse or the Twitch app.
All this does is provide a way for an addon author to create zip files of alpha builds. If the author switches to Beta, then alpha builds will not be zipped up. If the author toggles Release, then only Release builds will be zipped and available as downloads.
This is true for both Curseforge and Wowace, and it is not unique to DBM; any project on either Curseforge or Wowace can be set to the preference of the addon author.
Which, as an opinion, bugs me that the author allows alpha builds as zips because then I get "your version is out of date" messages when I join groups and raids, when in reality, while technically true, the author is still making changes and DBM is not ready for the masses. But that is just me.