Op-up on flight not originally booked in? How often?

[pilot]

The other day I flew HKG-SFO. Originally I was booked in business class on CX870 leaving at around 2pm but when I checked-in on the day of departure the agent offered something rather surprising (or perhaps surprising to me since it has never happened to me before). She said that business class for CX870 that day was overbooked and said she is willing me to upgrade to F. Ooohh? Really....I thought? But the catch is that I will not be upgraded to F on CX870 but rather on the later CX872 departing about 2 hours after 870 through. Without a hinch, I immediately grabbed the offer. :p I mean unless you are going to miss a connection if rebooked to the later flight, who is going to resist this offer? :D

So for a small sacrifice of arriving 2 hours later than I intended into SFO, I ended up getting a grande prize. Both 870 & 872 that day was using the 74A, so not only I got the upgrade to F, but I also got the new seat (which BTW was my 3rd time with that seat). And do I ever love the new seat! ^

So does this often happen quite a bit where you are being offered to be upgraded but upgraded to a flight that you were not originally booked on?