They are being treated equally. A citizen of France who is resident in Luxembourg would be able to purchase. A citizen of Luxembourg who is resident in France, wouldn't.
You can have rules that apply only to residents, but they have to be applied to any resident.
Maybe I'm missing something, but Germany's personal car toll system was supposed to be offset by a rebate on car taxes that would benefit any resident (or more precisely: anybody paying their car taxes in Germany) and was found to be in violation of EU regulations. Are there special cases for tax rebates or what would have been the difference?
You can have rules that apply only to residents, but they have to be applied to any resident.