Plastic injection moulds cost a fortune, but Resin/metal moulds are a lot cheaper.IIRC, the big push to switch to resin now was due to a new development that would allow GW to use the exact same molds that they were using for their metal lines and now use them to create resin models (some tweaking of the molds was necessary). There is no way GW made entire new molds for the Finecast line, at least not in any volume, because the price hike would have been much, much higher (molds cost an arm and a leg).
the thing that makes me think they have possibly made new moulds is the fact that a fair few of the new miniatures have been laid out on sprues and on some miniaturs its spread across two such as malagor. A long time ago i saw the prcoess at a GW demonstration and most of the parts for a miniature were part of a circle mould ( the metal process). either way would be interesting to know for definete if they made new moulds or not.