I experienced the same thing this and last season. My hypothesis is that it comes from the full body involvement and bc your upper body is not so trained yet. Using the whole body lifts the AeT and this is why it feels relatively easy. After a few runs, my Aet returns to normal levels again.
This early summer I tried to rollerblade with poles and my breathing AeT was almost 180 bpm while my AeT for running and mountaineering is 165. After a few rides my AeT reverted to 165ish.
I stay below my default AeT for Z1/2.