… most dictionaries record that the word tea is also used to refer to other plants beside the tea plant and to beverages made from these other plants. In any case, the term herbal tea is very well established and much more common than tisane.
Furthermore, in the Etymology of tea, the most ancient term for tea was 荼 (pronounced tu) which originally referred to various plants such as sow thistle, chicory, or smartweed, and was later used to exclusively refer to Camellia sinensis (true “tea”)
I think the confusion come from the fact that in many languages and cultures the name for tea and plant infusion is the same. Tea is name plant infusion because it is among the go to infusion if no plant is mention. But then in these language the name for “herbal infusion” or “herbal tea” does not contain the name of the specific plant “tee”. This or the languages got it wrong. Yes, I go that far.
From https://en.m.wikipedia.org/wiki/Herbal_tea :
I think the confusion come from the fact that in many languages and cultures the name for tea and plant infusion is the same. Tea is name plant infusion because it is among the go to infusion if no plant is mention. But then in these language the name for “herbal infusion” or “herbal tea” does not contain the name of the specific plant “tee”. This or the languages got it wrong. Yes, I go that far.