That's likely the size of the entire checked out tree, which would include all of the files.
I just ran the command here and my AOSP 11.0 checkout is 54GB, minus any git history, since I clone from a local mirror and use '--reference' to avoid having to copy objects.
A lot of the size here is from the various prebuilts, AOSP build is quite self-contained (jdk, clang, etc) and barely uses anything from the host.
https://source.android.com/setup/build/downloading
Although, an answer at https://stackoverflow.com/questions/33053615/how-to-download... from October 2020 says that even a partial clone is still 73 GB in size!? That’s insane! How the heck come it’s so big?