I have a theory. What if this isekai isn't really an isekai, but rather, just a dream he has while being in a coma from the body trauma from getting hit by a truck?
Think about it...
1. He was just shitting around maling random stories, yet he somehow actually got the whole Diablo cult correct.
2. Lots of plots are revolved around the mc directly.
3. Etc, you get the point