Free upgrade to premium economy

First time flying Starlux a few days ago with a group of 4. At the check-in counter, we all got upgraded to premium economy on JX712 (SGN→TPE). I was pleasantly surprised. Does this happen often?

I booked through Alaska where I have MVP status. Maybe that was a factor in the upgrade.

We also flew JX32 (TPE→SEA) regular economy.