What makes for an 'Intensity' day - outside trail rides?

I notice that my outside unstructured trail rides have a relatively low TSS when I am riding less pedally , but technical rough trails. Per the Garmin I am still hitting high HR and Breathing rates, and it’s training metrics will label the ride as intense ie Tempo or Anaerobic. So is this still an ‘Intense’ day due to Heart and Breathing stress combined with the more full body effort? Not to mention the mental stress of picking lines and keeping the bike wheels down.

It’s just a different type of training that’s all properly more punchy and being explosive so still good stuff