I found the answer to my question and the reason behind the response of MNTA IR saying "both are correct":
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From MNTA IR:
The Goldman report states that we received the request in the form of a “non-approvable letter” and responded in the form of a “minor amendment”, both of which are correct.
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FDA has eliminated the terms "approvable letter" and "non-approvable letter" sometime in 2008:
As MNTA received the letter before this time, it was still called a "non-approvable letter" and as MNTA responded after the elimination of the terms, it responded in the form of a "minor amendment" to suit the new term of the letter, i.e., a "minor deficiency letter".