I was asked the following question:
For the repetition of the Shemone Esray, you need only 6 to finish praying to begin the repetition.
However, there must be 9 people answering Amen to the blessings. Why?
What can I answer him?
Tefillo K'hilchoso 13 (27) says (my translation)
Ideally (lechatchilo) one should not start the repetition of the amidah with less than 9 excluding the prayer leader (from the expression in Sh O 124 (1)), because if there are not 9 listening the blessings of the prayer leader are close to being in vain (levatolo). But there are those who are lenient and allow the repetition with 7 or even 6 who have finished (Mogein Avrohom 55 (8)).
This information is very similar to the answer to Quorum for chazaras hashatz because the question is very similar to that question.
The answer to the person who asked the OP is therefore:
The first statement in the question goes according to the lenient view.
The second statement goes according to the ideal view.