When a moderator replies to your report and we decide to send a message, that's how it's sent. When you get a notification from someone without a username and it says your report was resolved/rejected/etc then it's from a moderator.
Basically yes we rejected this report because it wasn't against our rules
p.s. while we will look at reports of old posts in case something really harmful was missed, i don't think it's helpful to go through old profiles and posts in general