It’s certainly interesting as we’ve discussed before and having recently adding a HR monitor to my ebike rides I’m getting more of an insight into how hard I have to work on one.
Can’t remember the TV show (might have been Top Gear, maybe not), but there was a segment where they put the presenter pillion on a bike being ridden by Guy Martin with a HRM.
The point being shown was that you can be doing an activity and it can induce a high heart rate, but that’s nothing to do with your metabolism.
Being driven round at 100mph on the back of a motorbike, watching a horror film, or riding an e-bike, might all result in your heart rate climbing to ~150bpm. However, that’s just adrenaline, nothing like going for a pedal-powered ride and getting the same heart rate.
Your Garmin might say you’ve burnt off so many calories, but it’s basing that on an assumption that your heart rate is metabolically appropriate, it’ll be significantly overestimating your work done.