I've had lots of guys come up and talk just to chill and be friendly.
Not all guys are perverted and looking for some vag to play with later.
That's what you THINK... but trust me... guys are constantly thinking of sex, when they talk to women... as has been pointed out, it's just how we're wired. If you're not getting that vibe, then either the guy is very good at making himself come across as non-threatening to you, or to be blunt, you may just not be his type.
Now, if we did have sex on the mind, and after talking to you, didn't get a good "vibe" from you that you'd under ANY circumstances be open to that, we may continue the conversation on a friendly level, but sex always enters into our minds... it's natural.
I know for a fact almost nobody would ever admit this openly, but suppose you have a guy friend, on a purely platonic level, like you grew up next door, and all that, and you just regard each other as friends. Well... if that guy finds you in any way sexually attractive, part of him WILL always be thinking "I wish I could be "intimate" with her", or "Man, she's so hot". Again, they will never say so to your face, and may even be ashamed to admit it to themselves, but the thoughts are there, at some point, on some level.
There was a TV interview recently with Steve Harvey, where he was talking about his new relationship book, and he had said that the moment a man sees you, he has a plan for you. I think that is true... we saw you, and liked what we saw, so based on that, we decided to approach you, and make the attempt. Nobody in a bar looks to a woman sitting at a table and thinks "Man, I bet she has the sweetest personality, and is the best person on the inside"... no, we think "Oh, wow, she's pretty... I'd love to meet her". When was the last time a guy came up to you in a bar, and wanted to discuss the benefits of ethanol versus petroleum, or the political landscape of the Middle East, or stem cell research? No, we want to flirt, and more, but at least flirt.
And before anyone jumps on me for expressing my views here, let me offer that the struggle to understand the opposite sex has been ongoing for as long as there has been civilization, if not longer, so women will have one viewpoint, and a man will have another. I am telling you what I believe and know to be the case, from my own experience as a man. Take it for what it is.