If the OP confirms their nationality, it may be easier to work out if there was an error or not made on the outbound flight
eg timatic shows for a German passport holder resident in the UK destination Hungary
"Nationals of Germany are allowed to enter with an expired passport or expired national ID card. These documents are accepted when expired for a maximum of 1 year."
whereas if you do the journey in reverse - "Passports and other documents accepted for entry issued to nationals of Germany must be valid on arrival."