I've only seem that term applied to accordions - the continental chromatic system is usually 5 rows of buttons but can be just 3, going up in semitones diagonally across the row.... but nothing to do with concertinas.
The only continental contributions to concertina design are the German part of the Anglo system - which is short for Anglo-German - and possibly the Chemnitzer concertina, which is an instrument with square or rectangular cross section instead of the usual 6/8/12 sides and which otherwise looks a bit like a large Anglo. (and plays a bit like one, I believe)