Here's my bet as to what they mean:QuoteWe used high precision CAD tools to design these two parts fitting together so water's natural surface tension would make it unlikely it will get in between and sneak up into the battery compartment.
They state, "The camera is protected…," not the camera + grip.
I just took a look and the grip has a raised lip around the battery area of the body and then another raised lip area where the battery compartment is - and this body / grip combo is much different than previous ones (note the cost). It's magnesium & engineering plastic just like the body and there is little if any play between the body and grip. I wouldn't trust it in a tropical storm, but I think it would be just fine in light rain.
Neither lip appears continuous to me, and looking at the sealing diagram I don't see a green line extending around the the junction of grip and body. There's one around the bottom of the camera, another around the top of the grip.
I agree that it would be fine in light rain…in fact, I pretty frequently see people shooting with Rebel/xxxD bodies in light rain. I actually think it would be fine in heavier rain, as long as you keep the gripped camera upright.