Heart rate even Whit no wearables

I have my phone set to no wearables but the sleep graph still shows the heart rate. That’s fine, but, is it normal operation.

If you have a wearable with HR that send the HR info to Google Fit, Sleep app with get this info from Google and show it.
I use Fitbit and when there was no support for HR yet, I could see the HR from Google Fit every morning in the Sleep graph.

Hope it helps.