Grout is not waterproof. Hopefully you have a complete waterproofing system under the tile. Grout can go in any joint as small as 1/16” (maybe smaller) post photos from further back as well as any that show the waterproofing.

I wouldn’t even say this is 1/64”, there’s no way sanded grout is getting in here beyond wiped along the surface. its a full schluter curb under here. Even so, we have decided to have them take it off and put the same quartz as our bench along the top of the curb.

@Hallett & Co., I understand that grout is not waterproof and apparently, sealing grout doesn't make it waterproof, either. We used an unsanded grout called Prism (by Custom Building) on our glass penny tile shower floor. If water penetrates the grout, is that okay as long as there is a waterproof barrier such as the Schluter System under the tile and grout? And if that's okay, won't the moisture be an issue if it doesn't dry out between the tile and the Schluter barrier?