Yeah that is not how it should have been handled. Nonoha asked a genuine question out of curiosity
(some possible jealous) and rather than talking about it with an honest reply like “I was worried about something and she provided advice” or “we can talk about it in more detail later” Chidori replied with something that strains and breaks relationships to this serious and direct question “it’s a secret”.
This is saying that she talks to someone other than her partner… and she is going to hide what they talk about and not tell her girlfriend. Could have been handled much better, so sure Nonoha is going to be a
child about it and act out. Who can really blame Nonoha though? She has a right to be upset at this point.