Myths about the Americas

Huckleberries are not blueberries!! Again, its a confusion of naming but the berries referred to that way are a similar plant of the same genus, but not the same species at all.

The wild blueberries are called "lowbush" blueberries. They are a smaller plant, with smaller berries, though they have a more intense colour and tend to be sweeter and more valuable by weight (better for making premium jams, juices or wines because of the higher glucose content, not as good for use whole). 

Highbush blueberries - the cultivated sort - are less sweet and not as valuable on the market since they aren't as good for making jams or juices. They are typically used whole, in baking etc (blueberry muffins and so on). You can make jams and juices with them, they just aren't as suited to it and usually need more processing and additives. If you buy a 100% pure unadulterated blueberry juice, it is probably lowbush.

In parts of the Maritimes lowbush blueberries grow in vast barrens, where they are the only plant that exists in that soil. Incidentally, there is one such expanse not far from L'Anse Aux Meadows.

If the Vikings hadn't seen actual grapes (only imported wine), they could see that the blueberries looked like bilberries but were obviously different and much better for making wine or juice. They would have known that these were not bilberries. They might have thought these were grapes, if they had never seen grapes - or maybe they simply used the closest word they had ("Vin") to approximate what it was that they found. Finally, they could have knowingly used the term "Vin" to refer  to the blueberries as a marketing ploy for settlers (the same way they named "Greenland" after discovering "Iceland" didn't appeal to settlers too much!)

Finally - if they found blueberries and really liked them (which is quite probable), what other name were they supposed to use? They had found a berry that was very sweet and highly suited to winemaking growing in vast abundance ... the easiest thing to do would be to call it a "grape", since grapes do of course come in many different sizes, shapes, and colours.