Its a jade goby very strange behavior for a jade goby, they are not ambush predators not very predatory at all they are omnivores who eat mainly veggies and sift through sediment in the wild searching for micro organisms and small creatures.
Maybe you should just switch to sand if he keeps it up. Ive had a lot of jade gobys none have ever been burrowers . My MARBLE SLEEPER GOBYS and my spotted sleeper gobys do it but never my jades or my snakehead gudgeons these gobys are usually more cichlid like in behavior compared to predatory gobys.