If you want the simple translation, then it is referring to what we would call "cups of tea" in English (although "two teas" is sometimes used, depending on your region). These are countable.
However, it could also be referring to 2 types of tea, "two teas," which is essentially uncountable. Duo would have put "dos tipos de té" if they were referring to this uncountable version, though.
In general, best not to overthink Duo's sentences, so just go with the simplest translation.