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Isn't the documentation that you refer to about *nested* list comprehensions, rather than list comprehensions with multiple 'for' clauses?
E.g.,:
 [number for row in matrix for number in row]
is not a nested list comprehension: it's merely a list comprehension with two 'for' clauses. But:
 [[number for number in row] for row in matrix]
*is* a nested list comprehension (a list comprehension for which the initial expression is itself a list comprehension), and there the advice to read from right to left seems to make sense to me.