@Flavio no, the fallacy of composition is the error of assuming that what is true of a member of a group is true for the group as a whole.
For example, Lebron James is the best player in the NBA so the Cleveland Cavs are the best team in the NBA.
In this question, the flaw is that the author is overlooking other relevant issues.
For example, while it may be true that caramels dissolve more quickly than pretzels, what about the sugar?
The correlation here is the length of contact with teeth for pretzels or caramels to result in cavities.
We cannot take this one category (i.e. length of contact with teeth), however, and assume that this means eating a caramel is less likely to result in a cavity than eating a pretzel is.
Hope this helps! Please let me know if you have any other questions.
