He may well be shy but don't be fooled. Despite the handshake, you are looking at someone who has been successful despite his reticence and apparent weediness. If you shake hands like this, learn to do it differently. You are telling the person interviewing you that you have little or no self-confidence and that you find it very difficult to deal with people. Unless you're looking to work for London Transport, it's high time you booked in for some remedial meet and greet sessions.
Some people shake only fingers.
This usually tells you that this person wants to keep his or her, distance. Men sometimes combine this with the strength of the bone-crusher. This will be a very painful experience, but remember, where there's blame, there's a claim. You can read the same signal from someone who grips your hand normally but ends the handshake quickly with a stiff hand that pushes you away. Either way, this person is not particularly interested in you.