That was certainly how I interpreted it, in exactly the way as you can’t do a C&D start at a land based airstrip with no parking spots. The water has nothing to do with it, but everything to do with the airport data.
I just quickly checked these three in LNM, and none of them support anything other than a “runway” start:
If they exist, they are few, and far between, so modders would need to include these in their sceneries to allow for it.