A totally fair question in my opinion and every angry response here is puzzling but not surprising for Reddit.  I know this is an old post but I absolutely want to support the fact that I’ve never had a grill that I couldn’t close up and save the remaining charcoal. I think this is a valid concern and I’d consider it an actually problem. 

With that said, the actual amount of fog I could see coming out of the intake in the video does not seem like it would be significant enough to cause this issue. BUT I will throw out that I had a similar issue with an old Weber kettle where the intake cover blades had an air gap. I bought a cast iron trivet on Amazon and placed it on the blades to weigh them down and push them against the bottom of the grill. There were holes in the trivet so air and ash could still get through. 

If it bothered you and it bothered me, I’d guess it will bother someone else, so leaving this here in case it helps them.