I just spent a few minutes looking for examples on youtube and got nowhere. I was probably searching for the wrong words.
I would say that if you're even asking this question, you know that there is something abnormal in the greeting. So this person is either being false or looking for attention. Now, when I say "looking for attention" it could be something innocent, such as that their cat just died and they want to talk about it, but aren't sure if they want to burden you. It could also be malicious, such as that they are trying to communicate that they don't really want to talk to you. Who knows? We can't put in good guesses from the information you provided. We'd need a video of it, really, and obviously you can't get that. But for you to make a thread about this, you already know that it is not a normal "hi."
If this is happening often enough to be a problem, you could make a point to ask the person, "How are you doing?" or "Is everything okay?" If they act like that was a strange question, you would then say, "Just making sure" and then you'd smile and change the subject. What this does is deflect any possible malice on their part. It clear that 1) you are noticing their abnormal "hi," 2) you are a nice person, who is concerned about others, and 3) you're not interested in any other reason for the abnormal "hi."