The longer grass was able to maintain a deeper boundary layer of warmer air, then your freshly mown shorter grass. The longer leaf blades helped the neighbors grass maintain a temperature over night that was higher then the frost point temperature. Your shorter grass, uniformly cut, lost temperatures faster then the neighbors, so your lawn frosted, theirs did not.
FA04 on October 14th, 2019 at 13:33 UTC »
grass is always higher on the other side
Genertaylorii on October 14th, 2019 at 14:12 UTC »
The longer grass was able to maintain a deeper boundary layer of warmer air, then your freshly mown shorter grass. The longer leaf blades helped the neighbors grass maintain a temperature over night that was higher then the frost point temperature. Your shorter grass, uniformly cut, lost temperatures faster then the neighbors, so your lawn frosted, theirs did not.
A cool example of environmental physics!
Thatblokeoffthetelly on October 14th, 2019 at 14:18 UTC »
The grass works like the hairs on your body... The longer it is, the more warm air trapped. The more you know. r/Eli5