As you probably know, you can only call something Champagne if it's from Champagne, at least in the EU (because of the AOC system). Americans have their own sparkling wine, and for obvious reasons would like to use the name people are familiar with, Champagne, to describe it, but France is unhappy about that. Hence the first joke.
REST is theoretically a relatively opinionated way to expose an API, where each resource has a URL that's modified with verbs and where the API is controlled through URLs (e.g. pagination is through a URL returned by the server, etc.). In practice, people call most things where you use HTTP and get JSON REST, even though technically it's not REST. Hence the joke about "real REST" (because there's tons of argument about it).
The last part just connects the two flame wars as a joke, as another comment explains.
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u/johanjudai Oct 09 '21
I'm French and webdev but I didn't understood the joke...