We had a couple of 'fine-toothed combs' discussions of this a few years ago on the "Devoted to Chopin" thread in ABF. Dr. Kallberg was in on it, and wrote out a possible guess of what that might be about. I'm skeptical about the 4/4 thing, and I suspect that this is one of those things that has gotten passed down a bit too unquestioningly over the generations despite nobody really being able to make good sense of it. (I don't think it has ever been written up any closer than second- or third-hand.)
For anyone who's interested, here
is a link to the more recent of those discussions.
Here's a 'for-instance' of how such a story might be incorrectly passed down. I don't mean that this is
how I think it was -- just a sample of how something like it could very well happen, and if you really want to know
....indeed I'd guess it was something like this.
Somebody (like maybe really Meyerbeer) says it sounds like 4/4 time. Chopin says baloney, you're misunderstanding it. Later, somebody else (maybe Halle, maybe Lenz who also often gets into the story, maybe both at different times) commented to Chopin how he was bending the rhythm -- maybe mentioning the 4/4 thing but mainly talking more generally about bending the rhythm in a way that it doesn't sound exactly like 3/4 -- and Chopin says, "It is a nationalistic trait." Which indeed it is.
By the way, when I listen to Horowitz's performances of the C# minor Mazurka, Op. 30 #4 (which is a different one -- I'm just using it as another example), that's exactly the reaction that I have. It doesn't sound to me like any meter that can be notated. In a moment of grasping desperation I might well say "it sounds 4/4" -- but it doesn't really, and it isn't really. It's just a very flexible rendering of the 3/4, which is so elusive that if you slow it down and try to count it, actually it does
sound more 3/4
than anything else (to me), but "in real life," which was the only way anybody ever heard Chopin, it's elusive.