Do you think that is more difficult than explaining to the students why they can’t use loops in their lua config files?

I wouldn't present it to them as "these config files are the same thing as Lua but without loops", but instead "these are config files and they have the same syntax as the Lua records we just learned about". And I would prefer that over "these are config files and they have a different syntax as the Lua records we just learned about." Although I can see merits on discussing that syntax differences exist between languages, that tends to overwhelm people learning their first language.