MP, Instant tourney, best hand South
Nothing in the explanation of North's double of 3♣ indicates that it is forcing. There is precious little in the explanation to indicate whether the double tends for take-out. If anything, inclusion of "2+ C" in the explanation suggests a willingness on North's part for South, if so minded, to convert it to penalties. For that matter, North does not hold the 2+ promised clubs, nor 13+ total points if you are going to be pedantic. Well, I let him off the 13+ total points. But perhaps explaining "takeout" instead of "2+ C" is both more helpful and more accurate.
It seems to me that either that double is wrong, or the explanation is inadequate.

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ing) tr. v. - Any bid made by bridge player with which partner disagrees.