What happened to my table?

I have an old table (end table-ish size) that has been in the family for years. It was made around the turn of the century as a wooing gift(Hehe they were practicle farmer type people). He wasn’t a carpenter or cabinet maker(Farmer), so it’s a little uneven, and a little wobbly, but it’s the kind of family thing that you kind of have to keep.

I use it as a nightstand by my bed, becuase I never usually put anything there, to protect it. It has some diamondy shaped slats as part of the top surface. I has assumed it was all the same wood because it’s all stained the same red color, but apparently not.

Anyway last night I was thirsty and put a glass of water on it before bed. I woke up in the night hearing a big crash, realized I had knocked it over, but was asleep again before cleaning it up. So now most of the table is just as it was, but there is a diamond shaped area that is completely grey, correspoding to one of the slats.

What kind of wood/stain combination causes it to be that volitile after a hundred years, while the stain on the rest of the wood is uneffected?

With a table that is that age I’m surprised the water from the glass sweating didn’t leave marks all the time. Many of those tables have inlays and veneers covering them. Often the finish was done differently to imitate another material, so it looked like there was inlay. This table either has a different veneer under that diamond or a finish originally was there in the shape of a diamond and a finish put over the entire piece because somebody didn’t like it a some point. Only modern finishes have the ability to resist damage like a sheet of glass covers the piece.