Those people are Very lucky you where there!
I believe all EPIRB's transmit your GPS position to the Search and Rescue Center, which in turn contacts the appropriate agency. But, I would not rely "just" on an EPIRB to save your life. IT IS a good thing to have and, at least that will give you a fighting chance of survival? But, If you really want insure survival you not only need an EPIRB, but also an approved offshore life raft, survival suits and some luck? A friend of mine, who went down off Cape Beal, was eventually picked up (by the Coastguard) in his life raft off Tofino and was after several hours drifting miles with the current! He did not have time to dawn his survival suit!
Depending on the call, the Coastguard's first response will probably be out of Tofino via helicopter and that is when weather allows! Then by boat/s and depending on where they are, that can take a few minutes, to hours? The Canadian Coastguard (which does a really good job and I do "float plan" with them whenever possible) usually has a ship offshore, but the question is where is it and where are you? For example, once where I thought I possibly needed a medivac, I gave them my coordinates and they advised it would be 5 hours to get to me? I was about 10 miles offshore between Bajo and Ferrer Point and in the fog. Yes, they have units spread out, but again the question is, where are they? Then, there are the many other factors that determine their capability of recovery (eg weather). BTW they can home in on a VHF radio signal.
From a prospective of someone who has spent a lot of time offshore on the WCVI? When things are not good… it is a VERY lonely feeling out there! When things turn bad, you really need to start thinking of your survival equipment, and very quickly!
Those two people are VERY lucky to be alive! And, there is absolutely nothing wrong with the buddy system!