As you are aware the REU-MAN was delayed. This was due to the aircraft operating a W pattern from manchester. MAN-REU-CWL-REU-MAN
Unfortunatly on arrival at CWL the aircraft had technical difficulties. TCX wanted the aircraft obviously to become servicable but it was a long fix and therefore TCX sub chartered a JET2 737-300 to operate the flight as the aircraft wasn't full on either sectors.
TCX once again trying their best to minimise the delays due to technical issues with aircraft no matter what the extra cost of sub-chartering a Jet2 aircraft.
Not sure how your experience was on the ground in regards to info but TCX operations had obviously came up trumps in trying to minimise the total delay to your flight.