From what I have seen the tape measure method is a joke. It almost always results in a heavier weight that what the actual weight is. Everyone I know that uses the tape method kills a dozen 300 pounders a year. Those that use a real scale might kill 5 in a life time. True 300 pounders are rare.....unless you weigh them with your tape measure.
What is actually taped or scaled and what is boasted are often two different things. Once should not confuse the two.
Agreed, I have taped and then weighed dozens of hogs to compare accuracy and YES there are hogs that will be 'off' considerably. But on average it is a reasonably close way to estimate weight.
Hogs that are taller and longer can weigh more than they tape. Pregnant sows can weigh more.
Some (less healthy animals) will weigh less. But all you have to do is 'adjust' for your region. In some areas of South Texas where hogs are not eating broadcast corn or protein feed, they can be quite raw-boned. Hogs in my area (Deep East Texas) are uniformly in good condition. I've seen and weighed so many dead hogs in 35 years of hunting them....that I can usually make a fairly close 'guess' at their weight before ever putting tape or scale to them.
Inexperienced folks tend to guess weights significantly higher than what the hog will actually weigh. Then you have your 'Boasters' who purposely cite a heavy weight. In fact, I would say the temptation to 'embellish' (by hog hunters) is exceeded only by fishermen. These are the same people that stand or sit 5' behind a hog for pictures....creating a 'forced perspective' that the animal is much larger than it is.