'Imagitarium Black Sand Aquatic Substrate sets the stage for a bold and demure aquatic environment. The black aquarium sand stands still as you set the surreal scene with iridescent fish and vibrant coral reefs. This fish tank gravel facilitates beneficial bacteria while offering fresh or saltwater fish a wonderful world.'
It's gravel, they mention it as sand and gravel which is confusing lol.
On both photos of the "sand gravel" (your and shop's) looks too rough for cories. Corydoras like to sift through their substrate, and their natural environment is made out of sand.