Why is this base?

I just had a hard 3h ride, as it was my tempo day. After 10-20 min warm up, I was constantly above Z3 - on the climb  (15km), I was in between zone 3-4 constantly.
Apart from warm up and cool down, my only zone 2 was downhill .Overall, 75% of the ride was in zone 3 and 4 - yet Garmin says it is base :( 

Quite frustrating, as I am trying to use Garmin coach - and it now recommends a threshold workout today, which i know I can't do, because I went full gas yesterday.
Not the first time it happened, many rides count as base - which then makes Garmin workout plan useless.

How is this computed? What would a threshold workout look like?

  • which then makes Garmin workout plan useless.

    I want to add to that saying I tried Garmin Coach and its "base" differs wildly from what I have set as my HR zones. My plan is almost finished (so we are beyond the peaking phase) and 4/5 times a week it calls for "Base 104-119 BPM" which does not reflect my zone 2 accurately. It is always asking for something <Z1 which, besides being nearly impossible/unfun for me to do, is also a poor use of time. I will not/cannot long ride ~112 BPM for 4 hrs. It's infeasible and I have tried finagling with settings to see if something would update. I would not use this feature again.

  • I have noticed when I upgraded from 26.18 to 27.13, two similar rides but one is classed as Tempo and the other Base.

    Firmware 26.18

    Firmware 27.13