Weed seeds and pest issues can technically be moved from one yard to another by mowers. Rinsing off equipment between lawns can be potentially helpful, but it may not be common practice for most companies. 

This year has been an exceptionally wet year, and we are seeing an increase in fungal issues. 

Based on these pictures and your conversation on the hotline today, it appears that the turf issue you have is powdery mildew. Here are some links about managing mildew issues in turf:

Turfgrass Diseases: Powdery Mildew (Causal Fungus: Blumeria Graminis - Formerly Erysiphe Graminis) (psu.edu) 

Powdery Mildew-Turfgrass | Yard and Garden (iastate.edu)

As noted in the above articles, mildew can occur more often in high nitrogen fertilized lawns. Before making any fertilizer applications this fall, soil testing is recommended. 

Here is a link to MSU's soil testing site.

Home | MSU Soil Test

Additionally, mowing higher can reduce weed competition, so it could stand to reason that the recent lower mowing in your yard has resulted in more turf weeds, like crabgrass. Here is recent article about the benefits of mowing at a higher height:

Raise the Mowing Height for Weed and Grub Defense - Gardening in Michigan (msu.edu) 

And here is a link to MSU's Gardening in Michigan page for home lawn care:

Home Lawns - Gardening in Michigan (msu.edu)