Unsticking a thread leaves a timestamp--everything requiring a save does. That's why they are called "edits". Quite simple, really, and something even you should be able to grasp.
While mostly done on the first post (I know I always do that), a sticky/unsticky edit is possible on any post in a thread since the property is actually set on a thread, not on a single post. In other words, if I do a sticky on the first post and Callaway an unsticky on another post in the same thread, my edit timestamp would remain on the first post while hers would be on that other one. I just tested it on my ask away thread, back and forth and on a couple of my own posts, and then on the QnA thread--go have a look.
I can't find a timestamp signed by Callaway anywhere in your old thread, however, which means that she unstickied the thread directly in her reply to MLA and so there wouldn't be an edit timestamp by Callaway, only the timestamp of her original post. Both use the same piece of code but are presented differently, depending on the state of the message itself.
As for your link, it would appear that you don't know how to do that sort of thing either.
Mine is a better explanation than yours because it is rational and explains what happened and how, rather than requiring a tinfoil hat on an idiot to be believed.
Now bend over, bitch.