This is not the same as tongue blocking. The rest of us cannot physically put our tongue into a tube no matter how much we practice. It is also more difficult for most people to learning the bending technique with this method. Tuning a guitar involves turning the tuning pegs one direction or another. Tuning a harmonica is done by filing individual reeds so that they vibrate either slower or faster when played.
Slower vibration makes the note lower in pitch and faster vibration makes the note higher in pitch.
In most cases, harmonicas will come already in tune and will not need any adjustment. A very high percentage of blues tunes have this as the background for the singing and lead playing. The act of curling your tongue into a tube to achieve a single note is sometimes called the 'U-block' or 'tube tongue' method. This is not the same as tongue blocking. The rest of us cannot physically put our tongue into a tube no matter how much we practice.