Filming can be tedious and boring, involving several months of shooting in the same location.
During this time, a small percentage of crews seldom arrange visits, essentially enclosing a group of people in a specific area, providing ample time to foster relationships. Besides that, all are charming men and women who have to act out love scenes, which can easily generate sparks, hence the existence of on-set couples.
This is too common, unless they want to hype things up, everyone won't find it strange and casually discuss it in private.
If it were someone other than Huang Mi, it wouldn't have raised any suspicion. However, Huang Mi is notoriously cold and aloof off-camera. Not just female actors, but even female producers or investors find hard to approach him. Simply helping Xue Feifei is in itself intriguing.