You’re not missing anything, but I would substitute the word improbable for impossible. It isn’t necessary for MNTA to claim impossibility for the lawsuit to be taken seriously by the Court.
it's impossible for TEVA (insert Amphastar if applicable) or any company to manufacture enoxaparin without violating certain of MNTA's patents during the process
Sanofi manufactures enox without violating any of MNTA's patents, so clearly it is possible to do so.
I'm guessing the delayed launch is simply because they got taken by surprise by the FDA action so they need to build stocks.