The question here really is SHOULD you leave an appliance running unattended. There is no reason why you can't do so, after all, it is automatic. There is most likely nothing in the instruction manual that says that you cannot or should not (is there??) Did the owner violate the manufacturer's instructions in any way by leaving the machine running without being physically present? Depends on what instructions are contained in the owner's manual.
I have been the victim of defective water valves on both my washer and my dishwasher. The dishwasher, fortunately was a GE Potscrubber, so when the valve failed, the overflow protection took over and the pump swtitched to drain mode to dump the excess water that was coming in. This went on for about 40 minutes till I came back inside. Fortuntely, the machine took care of the problem for me, otherwise the consequences would have been ghastly. My washer, also a GE FilterFlo was, fortunately, located in the basement. The water ran for about 3 hours (I was actually home, upstairs, asleep). It did a lot of damage to the basement, and everything down there had to be thrown out that couldn't be dried out. It was a mess. Washers (except for maybe Miele) have no such overflow protection, unless they are mounted in a pan with a drain connected, as that machine probably should have been if it was on an upper floor of the condo.
So, should you leave these machines running when you leave the house? NEVER. Not unless you can guarantee that nothing will ever go wrong with them. And no manufacturer can, or does, make any such guarantee. In this case, the manufacturer should have NO liability unless it can be shown that this is a regular and known defect that the manufacturer has been unwilling to remedy. Equipment failures happen (don't we all know that!!), it has to be up to the user to exercise good judgement in how that equipment is used or allowed to be used by others.
Just my humble opinion (and experience).