How was she supposed to know that he was planning to clear it off? 

Having a neighbor who is willing to shovel and plow all of the snow off the driveways in the neighborhood might sound enviable. Nobody really wants to spend hours of their day making their driveway drivable and hurting their back in the process, so if someone else is willing to do that for free, you might be eager to pounce on the opportunity. But the desirability of such a service depends on the neighbor’s ability to complete the task successfully. If he moves all the snow from your next-door neighbor’s driveway into your front walkway, that’s not actually solving the problem. At best, it’s impolite, and at worst, it’s malicious. Would you blow your autumn leaves into your neighbor’s front lawn? Maybe you would, and if so, you’re a bad guy! 

If your neighbor starts mowing your lawn without even asking you, it sends a very different message than him offering to do it out of the kindess of his heart. His actions heavily imply that you are not good enough at lawncare to take care of your own lawn, so he had to take matters into his own hands. I’m sure there are a ton of suburbanite dads out there who wish they could mow their neighbor’s unruly lawns, but they won’t do it because they know it’s kind of insulting. If you choose to take such a drastic step, you have to be sure that you’re okay with your neighbor screaming at you, «GET OFF MY LAWN!» If you can’t handle someone questioning why you’re tending to their property without their permission, you shouldn’t be doing unsolicited yard work.