He coached tackles and TE at UM in a bizarre o-line arrangement. Drevno coached o-line and was OC. According to a Detroit New article of January 2, 2018, "The offensive line has been the issue for several years, even before Harbaugh’s arrival. This season, Michigan ranked 91st nationally in tackles for loss allowed and 110th in sacks allowed. " The same article notes "All fingers are pointed directly at the offense, which is coordinated by Tim Drevno, who also coaches the offensive line, and pass-game-coordinator Pep Hamilton." By the way, I believe both are gone. So, in short, I am not sure Harbaugh's comments can imply a firing of Frey because of poor performance. The situation can as easily be viewed as Frey getting out of a bad situation. As a side note, he was a Broyles Award nominee in 2015.