To add to what rescdsk
said above, people interpret the same flirtatious activities in different ways. I've known people who think that hugging
has some sexual overtone to it. I've known people who have thought that a guy placing a hand on a girl's shoulder or something like this is somehow sexual in nature.
On the other end of the spectrum, I've known people who can do basically anything short of intercourse and not interpret it as sexual. For example, there are several people I know of (as opposed to know) at my university who are close friends and seem to have a tendency to make out just for the fun of it.
On a related note, just because something is romantic doesn't mean that it's sexual.
One of the problems with human psychology is always trying to draw a line between what is romantic, what is sexual, and what is platonically friendly, and then figuring out how it all fits in. If a friendship is between members of the opposite sex, it seems that even if it's platonic it needs some kind of romantic component or it will eventually burn out. Women usually don't like being treated like "one of the guys", and guys don't like being treated like a platonic girlfriend.
Then again, one has to define romantic. What a mess.