multisite subblog with no user? what does it mean?

was just going through my super admin "sites" backend and noticed a few subblogs with no user associated with them. what does that mean? most of my users are creating subblogs with similar names as their username.

for 1 subblog, i cannot find the username and i think i recall a user signing up a username at one point similar to that blug. anyway, the blog is still there, but no username associated with it.

in this case, i am imagining the user somehow canceled their username? but i have no idea how they would actually do that. (i know users can delete their blogs, however. see below)

for another subblog, i can find the username that most likely originally created the subblog. he's still a member, but for some reason his username isn't associated with his subblog.

in the 2nd case, is this user able to log in and go to their subblog dashboard still?

for both subblogs, i checked their dashboard and Users menu and found no users!

how does this happen?

i thought maybe the user deleted their blog, BUT i have tested and seen what happens when a user deletes their subblog. as expected, under the super admin Sites menu, the subblog shows up highlighted in red with a little "deleted" note, so i don't think that's what's going on.