In this Livestrong article they make a distinction between "fruit teas" and "pure fruit teas". The only difference i picked up on is that pure fruit teas have more sugar. But dont fruit teas also have sugar? Im confused.
Teas made with fruit and herbs, or fruit and tea, are often referred to as fruit teas. Teas made with only fruit would then have to be called pure. However a quick look online suggests that "pure fruit teas" also includes some of the former.
The article you link seems to use pure to mean "not containing tea*, as it discusses caffeine quite a lot. The sugar aspect is probably a distraction as even a fruit tea made by soaking dried fruit in hot water can only deliver very little sugar as the total weight of the dry tea is small and most of that is discarded.
There is no single standardized meaning of the word. You can take a guess at what the author of a specific text wanted to express with it, but you cannot tell for sure unless a definition is given more or less directly.
The article you are reading does contain such a definition, as it says that
Pure fruit teas are [...] infusions of fruit extract or juice
As opposed to teas which also contain herbs, spices and tea leaves beside the fruit. This is just valid for this one article though, and other texts may use their own definitions.
I assume that Fruit teas contain artificial or natural flavourings and other ingredients which I would not want to consume. Natural fruit teas may also contain unwanted elements, though I think to a lesser extent. I always read labels. Note: fruit contains sugar of which the amount will be shown on the info label.
If you read the article carefully:
Fruit teas are hot beverages that contain real fruit juice alone or infuse the sweetness of exotic fruits with earthy teas, herbs and spices.
Pure fruit tea:
Pure fruit teas are made from infusions of flavors from the juice of fresh fruit such as apple, cherry, raspberry, blackcurrant, blueberry, orange, strawberry and peach.
Conclusion: Pure fruit teas are infusions only made from fruits. While a 'fruit tea' is required to contain fruit, but may also include other herbs and flowers.