They'll be able to tell you what it was depending on what it was. Make sense?
I can tell you what it WASN'T. It wasn't your gas cap.
If it was speedo only, and the bump was related, it COULD be a diff pin or other trans issue in that general area of the VSS. Something to keep an eye on (fluid color). This would probably NOT set a code this early on. It must get much worse first.
If it was a power bump (temp loss), you probably won't throw a code either, but you're better off checking for them FIRST, so you can whittle away at it.