i missed the second part of your post. if it is their tree then its kind of fair.

i think when i visited family on thanksgiving my neighbor did that to me. i think they trimmed the branches that were reaching over their property. i came back and the branches and leaves were on my yard. i wasnt mad, im renting so whatever. i was planning to go get them to put them in the trashcan but a few days later they were gone lol