If true then that is what it appears to be. Also if true (and remember part of it is my conjecture added on to Gurman prediction) we still don't know the recharge times. It could be (from 0% to 100%) 2 hours for the metal and 4 hours for the plastic (or throw in your own mix/theory). So it may not be that big of a deal. Also you could just buy the metal puck if you need the faster charge times.
Here's the relevant paragraph from Gurman's report:
The company has developed both plastic and stainless steel versions of the circular charger, potentially one for the $349 aluminum and plastic Apple Watch Sport, and the other for the higher-end models. Its unclear at this point whether the company will sell multiple versions of the charger, as Apple has only shown the metal variant, though the Apple Watch Edition is said to ship with a special box and charging dock that may incorporate the stainless steel MagSafe connector.
I don't see the connection to charging times. My though after reading that paragraph is the plastic charger is cheaper to make so it might ship with the sport watch. Or perhaps Apple determined it's not worth the effort to produce two different chargers that essentially do the same thing and decided to go with the SS charger because it looks nicer.