It's really unfortunate when you need to be wary of helping someone out. I was also told, at least in Tamaulipas where I lived that it was unwise to help anyone who is injured unless they ask for help. If you help without being ask, you're liable for them and obligated to take care of them even financially.
A few years back I had a single vehicle accident between Puerto Penasco and Sonoyta. I hung upside down for about 2 1/2 hr. by the seatbelt in my pickup. When I came too, I saw two sets of feet standing in the grass outside the driver's window right along side of me. I heard two voices talking. I said, "Hey guys, I could use a little help here." After I remembered where I was, I ask them for help in Spanish. They immediately reached down, un-snapped my seat belt and took me out of the truck. I don't know if they were waiting for me to ask for help or not.
The Cruz Roja (Mexican Red Cross) took me to the border where I was transferred to a US Red Cross Ambulance that took me to St. Joseph's Hospital in Phoenix. I had to pay for the US ambulance ride, but there was no charge from the Cruz Roja. I made a small donation, and I donate every time I see them collecting on the road. I encourage others to do so also.