It has always been the standard SWTOR style : when you speak to a companion and a flirt option appears that is a flirt with the companion you actually speak.
At the end of Chapter-9 you speak with "Theron" in the cantina. And two option comes with same text, both are the same choices except one have a [flirt] in the end of line. Out of habit, without even thinking, I selected first one because I didn't want to romance Thereon but Lana. Bitterly I did it on all my characters.
After following discussions about why romance is not triggered with KotFE companions I realized that flirt option was actually for all companions. This is a very new and ambiguous way of starting companion romance even for a veteran SWTOR player. Not sure if I will have a chance to fix this later but please Add New Opputunity to Romance with Lana.