Sure it could be due to chemicals- probably an herbicide.

Looks like a mild case of glyphosate.

Glyphosate damage during the growing season doesn't look like that.
This image shows green veins with white tissue between.
Glyphosate during the growing season 1st affects the newest expanding cells -- at the base of the lea -- turning those cells yellow.

OP said "Our landlord runs a landscaping company..." he used an herbicide not available to home users.

Might be herbicide damage but still pretty cool!

Maybe you could be the first to make a Dandelion cultivar for the landscaping industry!