I read that article also - had to reread it 2-3 times to figure out why he used the word Inertia. I believe he was incorrect. I believe he was talking about the weight of the wing, which makes more sense to me. Inertia is not measured in units of force, so it cannot act against Lift.
So reread the article, and just insert wing weight in place of wing inertia. I agree with OTRCMAN's conclusion, about the author having to condense many details into a simplified explanation. Using the term inertia confused things.
Added: I also presume this to be wing weight and not aircraft weight. Why? Because if one uses his diagram and want to use those numbers to calculate wing bending loads at the wing/fuselage intersection, wing weight would be opposing lift. I would typically leave that entire term (wing weight) out. It's probably a magnitude (or more) less than the lift, and will provide you a more conservative answer.
Last edited by Ron S; 01-17-2019 at 08:40 PM.
Reason: another detail added