I think the friend was definitely unfair. He was offering $10 an hour, with an estimate of 5 hours for the job. That estimate should include reasonable breaks - going to the bathroom, eating lunch if the work period covered lunch time, plus breaks. In many areas.
The work itself sounds reasonable, if not pleasant, given what you already know about the family's basic housekeeping skills. But for the first day, the friend should have payed $70 without question. As it was, he under payed, and had the nerve to complain that they hadn't put in a full day's work yet.
However, taking on the job for a second day, without control over your own transportation, was not a particularly sensible thing to do - the results could easily be predicted. And I'll predict that he will get under payed for this job too, when he's eventually allowed to leave.
Teaching teens to take responsibility for their jobs, and follow through on what they'll say they'll do is important. But I would also teach him the difference between a favour and a job, and that there are three situations where you can walk away from a job immediately, regardless of what you promised.
1) Your employer is asking you to do something illegal or unsafe.
2) Your employer is physically or mentally abusive
3) You arrive and find that the terms of employment have been changed from what you initially agreed to. This includes changing the salary, or expecting you to work for free.
Teens are often taken shameless advantage of in the workplace, because employers know that they are often ignorant of basic legal work rights, and because teens are used to having to do what authority figures tell them to, even when the instructions are unfair or don't make sense.