Makes sense if he was a stray. Kittens get used to human touch and friendly petting between ages 6 and 12 weeks; or so I've heard. If he didn't get much human contact during that time, then he is not used to trusting humans, and may have even learned they hurt him at times. So he is warning anyone who approaches to watchout, he is a mighty tiger!!! Once you start petting him, he knows you mean to be friends and he settles right in to enjoying the feeling of nice gentle petting. Over time, he will learn that is what YOU represent. He may or may not accept all humans, but he will accept you. Just keep talking to him gently and softly and giving him the petting he craves!