lua/lua5.2/lua5.3 do not provide /usr/bin/lua
The Lua packages do not appear to provide /usr/bin/lua. Only lua5.1 provides the binary.
If you apk add lua/lua5.2/lua5.3 by themselves without lua5.1 you do not end up with /usr/bin/lua.
This could be by design, but it appears (at a glance) that the APKBUILDs are supposed to relink the lua binary to the latest version installed.