Unless you have a different page in mind that shows the mistake you described, I think the DB's entries on Infernape's tutor moves are correct. You must be viewing details for the wrong game, as I can find Stealth Rock on Infernape's list for both B2/W2 and OR/AS which are the only games Stealth Rock is a tutor move. But the pages linked there default to B/W and X/Y, so you'll need to toggle which game you're viewing for the correct info.
I think you are onto something with the actual egg moves list for Bisharp and Pawniard though, as they're shown to have only have two compatible parents for Stealth Rock: themselves, which as you mentioned is incorrect since the Infernape line can breed Stealth Rock onto Pawniard. However, I'm not the sure the extent at which this is incorrect -- Bulbapedia says in its lists for every generation, which include the Infernape line, that Pawniard can only inherit Stealth Rock from a Pokemon that "learned the move in an earlier generation", which adds a layer of complexity to this. I guess it might explain why it's missing on here -- though it seems Serebii is missing it too. Pokemaster (who edits this site) is probably the only person who could really explain what is going on here. I'll leave this answer here until he's able to offer some insight.
