Oh come on. If it wasn't intended to be an "attack," then why was his answer the exact opposite of his answer a few months ago (when he said that lawyers had looked into it, and there is no issue with Cruz)? Trump was trying to stir the pot with innuendo about Cruz, and you know it.
(Notice how, to many Trump supporters, anything negative said about Trump is an "attack," while anything negative said by Trump is just "answering a question" or the like?)
If circumstances were different and Cruz could have used this same issue against Hillary, we would have had endless posts extolling the Constitutional Brilliance displayed by the only conservative in the race.
Flexible morality is so useful in winning arguments.