Authorial intent in the first panel is artistic license.

I WOULD take as given that people would assume that, but there are legitimate canon reasons to wonder "hang on, does that mean something? Is that important?"

It's IMPORTANT because startled cat-like Ellen needs to be a thing, darn it!

"Doesn't Mean Much"

I wanted to acknowledge Ellen's initial reaction to some random guy approaching her, and her not getting any creep-vibes from Larry, but I ALSO wanted to acknowledge that Ellen is not, in fact, psychic, and doesn't really know what Larry is thinking.

This is why one shouldn't really take it personally if they're a stranger to someone, and that someone isn't immediately comfortable around them. There are people out there to be careful around, and that someone doesn't have enough information to conclude anything yet about the stranger talking to them.

If uncertain of who a person is dealing with, someone effectively responding with shields up is not unreasonable.