I could be that the slope of his property is forcing any runoff down his foundation, making his sump come on. Also the water coming out the hose may be going right back into his basement, again causing the sump to come on.

Does the water being expelled look dirty or clean? If it is clean then your neighbor may have a broken water pipe with the runoff being collected in the sump pump.

Was the sump running before the neighbor left for a week? If so did you talk to him about it? If so, what did he say about it?

You stated that this âÂÂIt has never done this in the previous years...and to add, MINE never runs in the winterâÂÂ
Have you had above average rain this winter?

It sounds like its either water entering from the foundation or a domestic water line break. I would try to contact the neighbor or a relative as soon as you can and not wait until he returns. (Even the water Co. they may be able to detect abnormal consumption)
If itâÂÂs a broken water line the damage will only get worse and your âÂÂice rinkâ will get bigger.
Good luck

You are not allowed to pump water into someone else's land.

Time for a nice talk.
t the hose rerouting worked than you just have to wat.

The frost depth is not infinite.
Below a certain depth (many feet in MN) the earth does not freeze and there is free water.

Scott, did you get to the bottom of the problem or at least get the flooding in your yard stopped?