Let's look at real examples. <https://bodhi.fedoraproject.org/releases/EPEL-8M> lists avocado-latest-820200512173744.9edba152 module. That's this <https://koji.fedoraproject.org/koji/buildinfo?buildID=3D1506528> module build in Koji. The Source field reads <https://src.fedoraproject.org/modules/avocado.git?#12e2140e759fdb0a4477ab2432c411a4452d8efc>.
Theat means "fedpkg clone modules/avocado" and there these branches:
remotes/origin/52lts remotes/origin/69lts remotes/origin/HEAD -> origin/latest remotes/origin/f29 remotes/origin/latest remotes/origin/master remotes/origin/stable
The module stream is called "latest", let us check "latest" branch:
commit 12e2140e759fdb0a4477ab2432c411a4452d8efc (HEAD -> latest, origin/lat= est, origin/HEAD) Author: Merlin Mathesius <email@example.com> Date: Tue May 12 12:37:44 2020 -0500
Rebuild with avocado 79.0.
Signed-off-by: Merlin Mathesius <firstname.lastname@example.org>
So you can see the module is built from a non-epel8 branch. An avocado.yaml file lists these dependencies:
dependencies: - buildrequires: platform:  requires: platform: 
So "platform" is left empty to expand it by MBS on all available platforms. If you look at koji listing <https://koji.fedoraproject.org/koji/packageinfo?packageID=3D26942>, there are five modules avocado-latest-*20200512173744 builds of from the same sources. That probably means that Koji attempts to build the module for all Fedoras and EPEL 8. Technically, it's possible to override the platform with "fedpkg module-build" command, but I cannot see any trace of it in the logs.
That build was performed by "merlinm" users. You can ask him for more details.