I've seen situations in the past where the same flight number referred to multiple flights between endpoints that had no apparent relationship to each other. I've also seen a single flight number refer to a flight from A to B to C, but used a different aircraft to get from A to B than from B to C. I can't find any examples at the moment though so maybe the airlines have stopped that particular insanity.

Also, airlines regularly make minor tweaks to their schedules. It's possible that what you saw was one of those tweaks taking effect.