Why did he ignore her?

About a few months ago my friend and I attended a banquet for a company that we both work for and all branches from each state had representatives that also attended. So anyway we met this certain guy who was the ladies man lol. We both have his facebook pages though I'm not on as much (too busy lol) and I guess we're now all mutual friends. When I did log on I saw that he flirted with her a lot on her page and she did flirt back as much as he did and expressed how she couldn't wait to see him again while commenting on his page everyday. And she told me how close they have gotten. However when we went to the next annual meeting for the company he pretended he didnt know her. He shook her hand while he was leaving but that's it. Me on the other hand, I didn't pay him any mind all night but he made sure to give me a hug and try to get in some small talk and gave me so much attention that I wasn't looking for. She became angry, but at me! Anyway, does anyone understand why he ignored her, did he lead her on?