The Apple Watch told him his heart isn't working right - automatically calling emergency services - and he also called his wife to let him know the watch says there is an emergency with his heart?
Or was it that he too passed out, the Apple Watch called emergency services, who resuscitated him enabling him to call his wife?
The watch will call emergency services, then it will text your emergency contact(s) and let them know you've experienced a hard fall. I don't know exactly how, in this instance, that was then converted to a voice call.
Edit: I see in another comment that he initiated a call himself because he was conscious enough to do so.
> Apple Watch cannot detect heart attacks. If you ever experience chest pain, pressure, tightness, or what you think is a heart attack, call emergency services immediately.
Development of a 12-Lead ECG Signal Processing Algorithm Using NI LabVIEW® and NI ELVIS: https://ieeexplore.ieee.org/document/8574627
You would most likely need a 12 lead ECG/EKG too, to detect it accurately.
Outside possibility is he felt bad, saw a heart rhythm notification, and manually triggered emergency sos by holding the power button. But a fall alert seems much more likely.
Aside: as others note, though, you can't really detect heart attacks well from something this simple.
That being said of course they will state that the watch can’t detect accurately hearth attack to avoid any liability.