Thanks things are working fine. I mostly use Ubuntu, I’m just trying out a different Linux flavor.
Bit late, but there is some history.
Initially, the CentOS Linux 8 repositories had directories BaseOS and AppStream.
The names of repositories in DNF config were BaseOS and AppStream.
CentOS Linux 8.3-2011 did rename the repositories into baseos and appstream.
The directory names (and hence URL) remain BaseOS and AppStream.
This obviously leaves open questions.
Why they [CentOS project] did not rename the tree?
Why AlmaLinux chose the same repo-name/dir-name spelling?
Buf-for-bug compatible? 
FWIW, Rocky Linux has the same repo id all lower-case, directories in upper camel case convention. 
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Well, we aim to be a drop in replacement and hence, we do not change anything which is the way it us upstream.