Are WhatsApp Accounts Considered More Private for Japanese Girls?

I met a Japanese girl at a social event, and she was sitting right next to me. When I asked if I could add her on WhatsApp as a contact, she gave me her Instagram instead.

My question is: do Japanese girls consider WhatsApp to be more private, so they prefer new acquaintances to follow them on Instagram rather than adding them on WhatsApp? I'm pretty sure she uses WhatsApp.