Let us see the article. Tongue movement and jaw movement, however large or small is an important part of embouchure manipulation. But a belief that simply making the oral space larger (or smaller) due to some "resonant" effect or "air-speed" effect is erroneous. There is little or no physical similarity beteween a thumb over the hose and the tongue inside the mouth if you examine the system as a whole. But if imagining or visualizing a thumb over the garden hose helps you make the correct embouchure them be my guest.