Intentionally sloppy code, like leaving exploits in the game. Like if perform some action in a very specific way, you trigger an overflow that unlocks an item that's otherwise very difficult or impossible to obtain. So rather than these exploits breaking you out of the intended flow of the game, it's a real game mechanic. Like having that unobtainable item unlocks a story path that changes the ending. I guess it's more like an Easter egg but it relies on typical game glitching techniques rather than extensive exploration.

In Halo 2, there was a level where if you damaged a banshee in a specific way and made it follow you down a tunnel, you could hijack it at the exact moment when a new level loaded at the end of the tunnel (otherwise you couldn't use it). Then you could fly up to the top of the level and find a modified weapon that was incredibly powerful (scarab gun). There was another secret weapon (energy sword) you could obtain by performing typical boundary breaking moves and walking on invisible walls. Normally, you'd be doing this to skip combat but the game was also rewarding you for it.