Have you worn a tampon? It’s the opposite of a plug. It absorbs the blood. A plug would simply, well, plug up the vagina, causing a build of said blood. The effect when you remove the tampon would be an absolute flood of blood.
The only time it doesn’t absorb is if you keep the tampon in after it has been saturated with blood, and let me tell you, when that happens it’s definitely not a plug.