A "reputation recalc" was recently triggered on your account. (This used to be something users/mods could do, but that functionality was removed in Dec 2013.) The sequence of events was almost certainly as follows. The upvote given on your answer and the corresponding reputation change were stored in the central database but somehow did not immediately trigger a visible reputation increase on your account. Later an automated process detected a possible discrepancy, recalculated and synced your reputation, and voilà! (Reputation recalcs have been triggered about 20 times on your account, and about half of these resulted in a change of shown reputation.)
In the future, I'd advise you not to take this reputation thing too seriously. If you feel a reputation discrepancy is persisting for a few days there might be a more serious problem that needs further attention. But not seeing immediate changes is something that happens from time to time, and shouldn't be a cause for great concern. As you see, the system did get there... eventually.