The Bug:

Sculk sensors are not activated upon quick actions in a boat.

Steps to Reproduce:

• Place an get inside of a boat.
• Tap the fowards key quickly. (W by Default).
• Tap the left key quickly. (A by Default).
• Tap the right key quickly. (D by Default).
• Tap the backwards key quickly. (S by Default). (No backwards movement is actually detected by a sculk sensor whilst inside of a boat. See See MC-210712).
  →  Notice how the sculk sensors does not activate upon doing any of these things, if you do them quickly enough.

Additional Information:

Quote from the 20w49a Changelog, "A vibration is anything that causes physical motion". I would definitely consider all of these as physical motion, as you are physically moving.