what is pkg annotation ports_top_git_hash?

Hi,

I'm looking into some metadata of a pkg.
I found annotation ports_top_git_hash which looks like what I'm looking for.

But I found that not all pkgs in one build have the same 'ports_top_git_hash'.

See for example:
curl -s https://pkg.freebsd.org/FreeBSD:13:aarch64/latest/data.txz | tar -x -f - --to-stdout data | jq '.packages[] | {origin: .origin, ports_top_git_hash: .annotations.ports_top_git_hash }' | jq .ports_top_git_hash | sort | uniq
"1b6eada811a"
"60a177caf14"

I found a reference to this in the poudriere source code, but it didn't make it more clear for me.
https://github.com/freebsd/poudriere/blob/b2360d43e63e098a9afd3243f81f7fe8852c8965/src/share/poudriere/common.sh#L1114

Wat does 'ports_top_git_hash' mean? Isn't it the git hash of the top directory of the ports tree?

Regards,
Ronald.