I assume you're supplying this as an interesting fanfic idea. As far as canon goes, I don't think there's any chance of it being true. Although it's cool, like you can say that since Snape knew Harry had seen his "worst memory" then he could build some stuff around it to make it more believable :P

But then, of course, there's Aunt Petunia saying in book 5 that she knew about dementors from "that awful boy, years ago".