looks like porcelain? Either way there is a coating on it and something sprayed on the surface affected it. The shine in the wiped areas is the same, and not affected, but there is clearly a color difference. This makes me think one of two things;
1. It's natural stone and someone sprayed something that damaged the finish enough to changed the absorption properties of the immediate area. The etch would have been obvious until it was wet, or coated with a topical
2. It's porcelain and it had a film, or was dirty, or had remnants of a previous topical that someone made a poor attempt to strip. The stripped areas are the lighter areas and the areas that were not stripped, or cleaned properly are the darker areas. Like a short person was stripping or cleaning it and couldn't quite reach the top, so they said screw it and coated over it.
Edit: Neither of the above options is right. I think this is natural clefted sandstone. Flagstone is the same thing, but flagstone only refers to the irregular shape, and can be sandstone, slate or quartzite.
If this is sandstone, then it was coated previously. Someone tried to strip it, but didn't get it all out. Topical finishes are notorious for sticking in the pores of this stone, and the old topical will show up a LOT more after you apply the new finish.
It wasn't stripped right the first time before the new stuff was put on. It needs to be stripped really well, probably a couple times, then re-sealed. You can also use an impregnator if they don't want the shine. MB-04 would be a good one .Very low odor, perfect for a small area like this.
