Using GnuPG 2.1.15 and command:
gpg2 --status-fd '3' --command-fd '4' --no-secmem-warning --no-tty
--no-default-keyring --no-options --no-permission-warning
--exit-on-status-write-error --trust-model always --pinentry-mode loopback
--armor --homedir 'test-keychain' --export-secret-keys
'8D2299D9C5C211128B32BBB0C097D9EC94C06363'
I got no NEED_PASSPHRASE in status
[GNUPG:] KEY_CONSIDERED 8D2299D9C5C211128B32BBB0C097D9EC94C06363 0
[GNUPG:] INQUIRE_MAXLEN 100
[GNUPG:] GET_HIDDEN passphrase.enter
From all tests in my suite only exporting private keys does not provide
NEED_PASSPHRASE.