A guy could be interested in you even if he does not speak at all. The issue has to do with how outspoken the person is. If he tends to be introverted, that is he gets his energy internally, then he may be interested, but may not know how to express it overtly enough to get your attention.
On the other hand a person who tends to be an extrovert, who gets their energy from interacting with others, is more likely to demonstrate his intentions.
If you really want to find out; you may have to make the first move. You can simply introduce yourself, and tell him how interesting he is to you, and ask if he wouldn't want to go to get a cup of coffee with you. He may be a slow starter.
Here is an FYI: generaly, slow burn relationships in the beginning, often are the longest lasting.