More BYU Alumi coaching in the PAC-12 than PAC-12 alumni

This is true.  There are three BYU alumni coaching in the PAC-12 than there are PAC-12 alumni.  But there are not many BYU alumni coaching elsewhere, and you can find PAC-12 alumni coaching all over the place.  The list of PAC-12 alumni elsewhere includes BYU's Bronco Mendenhall who played college ball at Oregon State.  Here is the list.

In the PAC-12

BYU Alumni coaching
Kyle Whittingham--Utah--Alma Mater--BYU
Mike Leach--Washington State--Alma Mater--BYU
Steve Sarkisian--Washington--Alma Mater--BYU

PAC-12 Alumni
David Shaw--Stanford--Alma Mater--Stanford
Jim Mora, Jr--UCLA--Alma Mater--Washington

Other schools
Rich Rodriguez--Arizona--Alma Mater--West Virginia
Todd Graham--Arizona State--Alma Mater--East Central (Oklahoma)
Mark Helfrich--Oregon--Alma Mater--Southern Oregon
Mike Riley--Oregon State--Alma Mater--Alabama
Sonny Dykes--California--Alma Mater--Texas Tech
Lane Kiffin--USC--Alma Mater--Fresno State
Mike MacIntyre--Colorado--Alma Mater--Georgia Tech

PAC-12 Coaches Elsewhere in College Football

Bronco Mendenhall--BYU--Alma Mater--Oregon State
Norm Chow--Hawaii--Alma Mater--Utah
Ron Caragher--San Jose State--Alma Mater--UCLA
Dave Christensen--Wyoming--Alma Mater--UCLA
Gary Anderson--Wisconsin--Alma Mater--Utah