Who wrote this article? Rockstar exclusively does in-engine trailers, always have. The only people looking for evidence it's in-engine still are too young to have lived through past R* launches, to see the trailers vs. game comparisons where the game ends up better (except ped density).
Another possible mistake has been spotted in the second GTA 6 trailer: during a short chase scene, a street lamp appears to float in mid-air. Rockstar is facing little criticism for this. On the contrary, some fans even see the glitch as a positive sign.