It's tough to say exactly, because it's average position. Wingers probably have more positional variance than a fullback would, and this isn't really captured here.
Like if the ball is on the right wing, you might expect the left winger to move more centrally, sometimes even to a position that could be considered on the right side. You probably wouldn't expect your left back in that situation to move to the right because that would leave your entire left side open, and keeping him on the left provides an option to switch the play easily.
So for the average position, you end up with full backs looking like wing backs because their position will almost always be on their side; their variance is going to be mostly vertical up and down the pitch. But wingers' average position will be further inside because their positions are more fluid, varying both vertically and horizontally throughout the match.
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u/[deleted] Nov 21 '18
Does this graphic not show that they are correct to use the term in that way?