Anytime an Instructor is giving Instruction, he is the Pilot In Command. To be Pilot in Command he must legally be able to be the commander. If he does not have tailwheel differences training then he can't be Pilot in Command.
Regardless of the fact that you were current on type, you were using the flight as an Instructional flight towards the revalidation requirements and as such should have been PUT. BUT as the Instructor was not legally allowed to be commander on the flight you did you were pilot in command and he was the passenger. As such the flight does not count towards your revalidation requirements.
Therefore you need to go and do a legal flight with and Instructor and have your logbook signed and then have an EXAMINER - Revalidation or above sign your licence.