Exactly my thoughts.

He was not asked to show his pasasport at Dublin and this was confirmed by cabin crew on the flight as he was concerned he would miss his connection to Manchester.
The Aer Lingus flight was delayed out of NY.
The cabin crew told him he would not have to go through immigration so he would have time. My son said it was wonderful as he just got off the plane and followed the directions to the departure area, so no immigration, no customs.
At MAN there was no immigration check.

My son did not even meet an immigration official

Not at all

Passport not checked at MAN either

Sorry should have quoted messages in replies