If you look at the whole section, it says,
5.5.3. Secret Key Packet Formats
The Secret Key and Secret Subkey packets contain all the data of the
Public Key and Public Subkey packets, with additional algorithm-
specific secret key data appended, in encrypted form.
The packet contains:
- A Public Key or Public Subkey packet, as described above
- One octet indicating string-to-key usage conventions. 0
indicates that the secret key data is not encrypted. 255
indicates that a string-to-key specifier is being given. Any
other value is a symmetric-key encryption algorithm specifier.
- [Optional] If string-to-key usage octet was 255, a one-octet
symmetric encryption algorithm.
- [Optional] If string-to-key usage octet was 255, a string-to-key
specifier. The length of the string-to-key specifier is implied
by its type, as described above.
- [Optional] If secret data is encrypted, eight-octet Initial
Vector (IV).
- Encrypted multi-precision integers comprising the secret key
data. These algorithm-specific fields are as described below.
- Two-octet checksum of the plaintext of the algorithm-specific
portion (sum of all octets, mod 65536).
and then it goes on to explain the algorithm-specific fields mentioned
in the second to last paragraph. But note that the very first entry
is a whole Public Key packet. This has the p, q, g and y values.
Then come the other entries: string-to-key usage octet, encryption octet,
string-to-key specifier, iv, and then the algorithmic-specific private
fields you saw. Finally a checksum.
Hal