Yes, all messages exchanged on Poparide are private and are only visible between you and the person you are sending the message to.
Previously, members could send "public questions" before booking but this feature has been deprecated as of April 2022 and all messages exchanged on Poparide are now private. A message being sent before a booking is now called an "Inquiry" and is private.
Note that for quality assurance and support purposes, the Poparide team monitors and may read messages exchanged in the scope of a trip.