It's the grain, Maple is very creamy and the growth rings are subtle as its a diffuse porous wood. Oak has the distinct madullary rays and is ring porous, (you can see tiny holes in the annual growth rings). If you google the above terms you should get some good pics.
To be honest though i know a bit of oak when i see it.
Now that you say oak has porous rings, I think it's probably oak. It does have those small holes in the rings.
Thanks!
Erd