Not so NOT SO,
Ldg gear monitor/ldg gear disagree is a NO DISPATCH status message. It cannot be deferred.
ASFKAP
The C of A would only be invalidated if the defect was written in the tech log and the a/c flown with it uncleared. As I suspect this was not the case then technically it was ok to fly.
Down route defects are quite commonly rectified by pilots talking to maintenance (Maintrol) to see if a simple fix will clear it and I suspect this occured this time. Redistribution of the hold baggage (BY BAGGAGE LOADERS NOT A HIGH SPEED TAXI AND BRAKE MANOUVER) is an acceptable way to ensure the nose squat sensor is in ground mode. Had it not worked I'm sure the pilot would have grounded the a/c.