remove the grass in at least a 2 foot circle... and then add mulch.. and then you wont be accusing hubby of weedwhip injury...

in fall.. move it at least 5 to 8 feet from the house.. this cute babe can get huge...

the damage could have been mechanical.. recall any ice or sticky snow bending that limb to the ground???

tree time is counted in decades.. a minor injury can take up to a year to 'show'... and very often.. the damage shows.. the limb dried.. when the heat of summer hits in july and august...

prune it out and walk away.. do not leave a stub ....

the other plant is probably coincidence... not really any facts to go on...

ken

My neighbor across the street had a Ponderosa pine seedling planted in his yard for over a year. He let the grass grow thick and tall right around the base as he watered and fertilized. One day he pulled the grass away from around the trunk, toward mid-summer. He found that the 1/2" dia. trunk has been completely girdled for 2" high, by small rodents. The tree died.

Certain animals have teeth that continually grow, and they gnaw on bark and other things to keep their teeth wore down and healthy.

I'm just adding this as a possibility of what might've happened to your plant.

https://www.canr.msu.edu/ipm/uploads/files/Community_and_Schools_PDFs/rodentfs.pdf

Voles (rodent) are common in Illinois. A possibility.