How does the activity app match duplicate activities?

I have recently been using the Sufferest cycling app which I post to Strava, while doing this I also log an indoor cycling workout on my apple watch 3 to measure HR. I was just wondering how the activity app then matches the two completely different workouts and adds the HR from apple watch to the Strava activity?


Very impressed but just wondered how.

Apple Watch Series 3, watchOS 4.2
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The Heath app on your iPhone combines health and fitness data from Apple Watch, iPhone and any other sources - such as third-party apps and accessories - that share data to the app.


When doing so, it automatically adjusts the reported results to avoid any double-counting of the same types of data for the same periods from different sources:


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