The Stryd app on your Apple Watch will show and record heart rate information (when privacy permissions are set correctly). The Apple Watch has an optical heart rate monitor built-in. This technology is not perfect and sometimes gives incorrect HR information. Stryd cannot correct the HR data and simply displays HR data as measured by the Apple Watch. If you are seeing odd HR data, it means that the Apple Watch provided odd HR data to the Stryd app.
You can improve your heart rate data by using an external HR monitor with your Apple Watch. Follow Apple's instructions to pair your Bluetooth HRM with your Apple Watch!