If you would like to prevent YouTube from disclosing information about your liked videos or saved playlists, you can choose to make this information private on your channel. This can be achieved through a slight modification of your privacy settings.
Keep Your Likes and Saved Playlist Private on YouTube
Sign in to your YouTube account. Click on the avatar located top-right > YouTube Settings (Cog icon), and then navigate to Account Settings > Privacy > Likes and subscriptions. Tick the Keep all my liked videos and saved playlists private checkbox:
Click on the Save button and exit the Settings page.