Perhaps it's a drip. At a glance to me, it looks like a minor finish flaw. If the wood surface wasn't immaculately clean before the early finish layers are put on, then the finish doesn't stick on hard; if that was the case and it got bumped, you might have lost a little chip of finish. The problem area got filled over with later coats which is why you can't feel it, but the absence of all the coats makes it reflect light differently.
I wouldn't sweat it as long as the finish on top of the spot is completely continuous with the rest of the top coat. If you look hard enough, you can ALWAYS find something that's not perfect, even in an Alembic.
David Fung
