Actually I don't know. I'm currently battling spam comments on this blog and today my main comment manager where I can see all comments wasn't working.
So I went through and deleted all but one of the spam comments. Then I tried my comment manager again, hit delete on the comment I wanted and it deleted everything. So I have no idea what happened there. Fun little glitch.
So that's why they were all deleted. I welcome your input so I didn't want you to think I was deleting your comments on purpose.
Have a great day!