Your neighbor stopped on a hill and what? Did he stop because all of a sudden the motor started smoking? Did it start running funny all of a sudden? Never saw any smoke before? Did you change the oil over on the hill or drive it back to a flat area, and if so does it run OK, or does it have less power? Has the amount of smoke changed? How long have you run it while smoking? 1 minute, 10 minutes, 30 minutes? Still smoking?
Yes, white smoke is from burning oil. Did your neighbor put 2 stroke mix in it by mistake? Change the gas.
You said you changed the oil, I assume on a level surface, and I assume you know how much to add and how to check it. What did the oil look like that you drained? Did you drain it into a clean pan and look for bits of metal? Why not?
Again, I assume you changed the oil on a level surface, because otherwise you'd overfill it which would splash too much oil on the cylinder from the crankcase, which might get past the rings and smoke. Check the oil on a level surface.
It doesn't sound bad, but the video has it running pretty fast. Does it idle smoothly. A quick check for worn or broken rings and or worn valve guides is a compression test - pretty easy on a small engine. If that rules out something broken, and the oil level is correct, it should burn off.