The relevant bit of the article your linked is "However, you might also want to try sliding your fork tubes down in the triple clamps a couple millimeters. This will slacken the head angle and make the bike more stable in a straight line and less likely to headshake."
While the author may have known what he meant to say, the way he has written it is confusing. You want to increase the rake angle of the front forks to increase straight line stability (think a 1960's 'chopper' style motorcycle). You can achieve that on a motorcycle by spring preload adjustment, both front and back suspensions. You want to raise the front of the bike (increase spring preload), and drop the rear (decrease spring preload). Doing so increases the wheelbase length and front forks rake angle, both factors in improving straight line stability.
P.S. sports type motorcycles use steering dampers because they are designed with short wheel bases and small fork rake angles so they can turn quickly. However, this compromises straight line stability, hence why steering dampers at fitted.