They are different languages
On PPCG we define languages based on their implementations, it follows simply that different implementations are then different languages.
This is a not un-problematic, because it also means that different versions of the same language (e.g. 1.5.1 vs 1.5.2) are technically different languages because they have different implementations, even if the difference is a couple of small bug fixes. This leads to the absurd result of being to use every minor version of your favorite language to repeatedly answer questions that ban using a language twice. We have to draw the line somewhere or we may as well allow repeats in a language.
I think that every question that is concerned with "different-languages" should define what they mean by different languages, based on the behavior relevant to the challenge and not rely on a PPCG wide definition. An example of this is the Add a Language to a Polyglot that only requires languages have different output on the program in question to be considered different languages. This works out very well for that challenge. Obviously it will not always be this clean cut to find a good definition.
However questions should in general avoid defining this based on "major" and "minor" versioning systems (I have been guilty of this in the past myself), because such systems are not universal. Not all languages have version numbers, and not all languages that do have them put the same meaning into the numbers they provide. Definitions like this should probably be based on the behavior of the languages, to keep things objective.