Nearly all bananas have a wax coating (the "powder" you note) along their pseudostems, and there's nothing uncanny or unusual about it. Some varieties have slightly more than others, but is an unreliable method for identification. Nor can you ID from the "look and shape" of the plant. Unfortunately, the only way to be sure is to see the fruit, which will have the characteristic deep blue/green color as it is ripening, in addition to being relatively small in size. This is possible in your zone if you dig the trunks up and store over the winter, then fertilize heavily during your growing season.

Another "clue" (but certainly not reliable for ID) is the much larger size ice cream can attain. Many dessert-types mature around 8-12 feet, but ice cream reaches 12-15 feet with leaves extending much higher. Since you have fewer light-hours in your zone, your plants may not grow quite this large.

-Bruce C.