Not quite correct IIRC.
From what I've read the USCG only considers it a "for-hire" situation if the compensation is a requirement of teaching or taking them out on the boat.
For instance, if you and two friends go out on your boat and you teach them some things about sailing, and they, being nice people, have brought a case of beer, $30 bucks for gas and lunch along, it isn't a "for hire" situation unless you REQUIRED the food, beer and money as a condition of taking them out and teaching them
Say you and three friends are sailing from Dana Point to the Channel Islands. Before the trip, you suggest that your friends buy all the provisions for the weekend trip and give you some money for gas, since its your boat. Again, this is not a "for-hire" situation unless you require that they buy the provisions and give you money for gas to take them to the islands. If they don't, my guess is that you need new friends.
If they forget and you don't take them... my guess is that they need a new friend with a boat.
Again... one last example.
You meet two people from sailnet, and they ask you to teach them to sail on your boat, since they don't own one yet. You tell them you will for 20 bucks and lunch... This is probably going to be considered a for hire situation. If they did own a boat, and you taught them on their boat for the same consideration, I don't know if it would be a "for hire" situation, since it is their boat.
As far cost sharing goes, if you take 2 people out with you and they pay the expenses you have created a for hire situation. However, if the expenses are shared in equal thirds then you have not.