Grimes was hired in DECEMBER 2017, FOR THE 2018 SEASON. It says so in his Wikipedia page that you are pointing to but clearly didn't read. Grimes did not coach BYU in 2017; that was Detmer's last season. If you are older than 3, you should remember that very well, because it was BYU's worst season in almost 50 years.
Roderick was part of Grimes' staff every year that he coached this past go-around.
Why you'd trust Wikipedia over the official BYU pages that were shown to you earlier makes no sense at all, but at least read carefully and make sure you get what is being said.