Having visited both Alto Piemonte and Carema, I can assure they are very far apart from each other. Alto Piemonte is located to the northeast from Langhe, an hour’s drive away, whereas Carema is situated in the almost opposite direction: geographically in the Aosta Valley, the Alps surrounding the village from both sides, yet sitting on the Piedmontese side of the border and thus belonging to Piedmont, not Aosta. The neighboring village of Pont-St. Martin is less than a quarter of a mile away from Carema, bot located in Aosta Valley, not Piedmont.
However, I can understand why Carema is usually grouped together with Alto Piemonte, since the style is very similar to the wines of Alto Piemonte and - unlike a great majority of Aostan reds - the wines are made of only Nebbiolo.
I guess this is the main reason for the mistake. However, “Alto Piemonte” isn’t a catch-all name for the northern reaches of Piedmont, but instead a well-defined region around the Sesia river, located at the northeastern corner of Piedmont.