Even if this was while running Cinebench, that's still representative of the "worst case" battery life scenario where his MacBook is constantly running at max load.
With my 2018 13", max load means about 3 hours of battery life. With my 16", it's about an hour (or less if I stress both the CPU and GPU).
I'd be very curious to see what battery life figure he's seeing when running Cinebench. If it's 4-5 hours, that means:
1. M1 seems to consume about 15W at max load, about 10W lower than Intel (AFAIK, MBP 13" is locked to around 25W sustained power consumption). Still impressive from a performance per watt standpoint, but not so impressive from a battery life standpoint. Also 15W means... there is absolutely no way the MacBook can sustain those clocks without a fan. Run about 10 loops of Cinebench to see if scores are dropping and we'll know.
2. If the range is 5 - 20 hours of battery life, a "happy medium" is probably somewhere in between. So I'd expect the typical user to get about 12 - 13 hours of battery life. That's more than what Intel MacBooks are getting, but... not mind-blowingly more like the quoted 20-hour figure. For reference, I do get about 6 - 7 hours of realistic usage out of my 2018 13". Apple's claimed "double the battery life" statement will still stand.
In any case, my M1 MBP will also land soon so I'll get to see all of these for myself.