It was 2014. They had an exceptionally poor receiving core that was headlined by Jason Avant, Donnie Avery and a Dwayne Bowe. Avery and Bowe were on their last legs. They lost 3 WRs who were on their roster the previous year.
Chiefs went 9-7 that season and had much better targets in Anthony Fasano, Travis Kelce and Jamaal Charles. They caught enough touchdowns for a winning record.
I'm not really sure it says anything about his ability to coach WRs or QBs.