@tailor31415, and i'm telling you there isn't anything really contradictory about Shuka's answer and the snake-bite awakening sigil power on people, hence your opinion about things being retconned is honestly confusing. The snake-bite could really just a trigger to a forced evolution on people. This is a manga we're talking about, an evolution happening in an instant is not unheard of. And also, considering multiple universe (server) is a thing now in this manga, alternatively, the Snake-bite could also actually just gifting people powers that their counterpart from different universe had managed to evolved to.
If you're referring to how the old man agrees more to Shuka's rather than Kaname's figurative answer of Snake-Bite, then that could easily put aside by the fact that the old man came from a Server that seemingly had a different concept for their D-Game, which isn't a "real-world mobile action game".