The stains are in the right corner and also I put a small drop in the middle of the stone

Yes looks like it etched. The more quartzite looks like marble the more likely it is that it will etch as the calcium carbonate gives marble its lightness but is also what etches when an acid touches it. Acid breaks down calcite. Many white stones sold as quartzites have high cabonite properties and do etch like marble.

That ain't quartzite.

I was told by the seller that it was quartzite so I tested a sample… and this is what resulted

" I was told by the seller that it was quartzite so I tested a sample… and this is what resulted "

Absolutely etching, and this is definitely more marble than quartzite as noted above, most white quartzites are closer to marble. And honestly the seller might have been told it was quatzite and took the wholesaler at his word.

Many of the "white" or gray quartzites are really dolomite/marble. They might be hard like quartzite, but are porous like marble/dolomite and will etch just like your sample. It would need to be sealed during installation and then at regular intervals. Sealing won't guarantee that you will never get stains or etching.

Turns out you know more about stones than the slab yard salesperson!!

Never believe what they tell you ... do your own research and testing.

Regular sealants will only prevent staining not etches. The Etch is not due to the porousness of a stone it is a chemical break down as acid eats through calcites. A resin like coating is the only thing to prevent etching.