Legal opinion? He is stating legal facts and what is enforced in his state followed by telling everyone to check their local and state laws.
The only one who is having a hard time understand this is you.
Also, manufactures don't assign payload values. They assign GVWR's (are regulated for various reasons) and subtract the weight of the vehicle leaving the factory which gives you the payload value. The tire inflation and load sticker was required per the TREAD Act on all vehicles made past 2001 to inform customers the recommended load limits of the tires. This is why vehicles prior to 2001 did not have these stickers and only had the GVWR and GAWR sticker.
When I worked for a few vehicle manufacturers, they would use EPA emissions and US DOT highways standards(like the chart in the link below) along with axle carrying ability to assign GVWR's to certain vehicles. Some vehicles were limited by their carrying ability and some were limited by the max GVWR of the emissions and highway classification they were in.
Vehicle Weight Classifications for the Emission Standards Reference Guide