They don't use the chips in the phones for triangulation. As I understand it...
You always have two towers you have contact with (in fact when you drop a call it is because you lost contact with one of the towers).
So they measure the signal from reaching the cell tower...translate the strength of the signal into distance you know you can figure out the point of the call.
In this case they had a ping from the cellphone tracking to one tower. So he probably determined the strength and calculated a radius around the tower to determine the search area.
Mostly what you do is you figure where half the distance to the next tower is, then make some adjustments for terrain.
Out in the boonies, you're usually only in contact with one cell site. In a more urban sitiation, the system computer is constantly making a comparison of signal strength from whatever repeaters you happen to be hitting. When any one of them has a stronger signal, your call gets switched over to that site.
Dropped calls are usually because NO site has a signal from you.
Both methods work on triangulation but with 911 the phone tells the 911 center where it is located instead of the cell company using tower triangulation. It is a GPS Chip and the phone triangulates itself via GPS. IOW it has the data and sends it to 911.
IWO if you dial 911 into a 911 system set up to receive the phones data from the chip you are located. Number 2 as I understand is basically the same thing I believe a second GPS chip which is optional use by the owner. Number 3 is the basic tower ping you mentioned and still effective but not as defining in exact location. I might be wrong. But this explains some of it also Cell Phone Pings I heard a rescue on the scanner one night several years ago and it sure impressed me to the accuracy.
If he has share location on they might be able to get his chip to tell his location or if they can by chance intercept a 911 call and the location data. Third option is him getting through to anyone anywhere and doing the towers triangulation. The GPS data if they can get it from the phone chip would be a sure bet.