Table finish unknown

I have a 10 year old wood dining table that was made by Keller Furniture Company. We love this table because if a water ring appears, it will dry on it’s own without leaving a mark. Unbeknownst to us before too late, water stood under a plant long enough to raise the grain. As always, there is no visible water ring, but the area is rough. I’d like to refinish this table to repair this, but don’t know what finish it currently has that allows it to handle water rings in this manner.

Does anyone know what this might be? Tung oil? Poly? Lacquer? Whatever it is, it has served us well!