The assumption was just on Kenny the Pirate's side so it's really unknown if they have a different reason for it, could be the shape of it much like TSA will screen things that make a certain shape.
That said I'm sure some people smuggle in but IF they actually are doing bottles including sunscreen they would basically be doing it like before because the amount of guests who bring in these items is pretty much everyone.
How would Disney even inspect this stuff on a large scale? I mean my collapsible water bottle is technically 100% always open, there was never a screw cap like a water bottle (there is a cap but it was never a sealed one), then there's the tsa sized bottle we use for hand sanitizer, for sunscreen, etc. None of that stuff is going to be closed. All of these things and more will 100% be open on just about every guests. I wouldn't mind if they need to have those gathered together in one bag rather than scattered about the backpack but to actually open the water bottle, the lotion bottle, the sunscreen bottle and the hand sanitizer bottle and that's just for 2 of us, I'm just envisioning it's a different thing they are doing/going on.
I'm not sure if they are really going about doing this for all guests that they would go through the headache of it just for potential smuggling of alcohol, but of course I could be wrong.
Keep in mind if this is just Epcot they are missing a huge chunk of people who take the monorail over.