Earlier quoted context omitted.
Those are urban areas. If you instead count by city limits, Berlin is bigger by a large margin [1]. This is the perpetual problem with defining "biggest" - to some the urban area of Paris might still be "Paris" but the vast majority of it is outside the city limits. [1] https://en.wikipedia.org/wiki/List_of_cities_in_the_European...
The urban area is what matters. Paris is larger than Berlin and the largest in the EU. Paris has the specificity of having small limits for the city proper but it does not make sense to use that metric for comparison because nowadays the city only stops at the administrative limits for adminsitrative purposes and nothing else. You won't even notice you've crossed the limit if not for the ring road. In fact, Moscow is…
It might well still be the biggest in the EU if you drew limits based on what people considered part of the city - I don't know - but it certainly would not be as big as its urban area.
In fact, I'd argue you're unlikely to find any major city anywhere in the world where most people would agree that every part of the outer boundaries of the urban area are part of "the city" (or even "a city"; parts of urban areas will still often be considered fairly rural by those who live there or in the nearby city) even in a loose colloquial or cultural sense. Even coming close would be exceedingly rare. This because the ways urban areas are designated by design tends to include commuter regions far outside, with their own identities, and often very separated from the biggest city in the urban area.
So while going by city limits will be misleading, so will going by urban area. Unfortunately, no single metric will be accurate for these things.