He's probably confused. You denied the ride home, which he probably interpreted as you not being interested, and then asking him to text you, he probably assumed was just a pleasantry like "we should stay in touch," but not feel you are really into him. He probably doesn't want to invest more of his heart assuming you aren't really interested.
If he is shy, you are probably going to have to be the one who makes the first move a few times along the way (not just insta). He is going to prefer clear signals, and even though you think you may be giving them, he will likely see other things as signals that may cancel them out (like you not wanting a ride), which will leave him in a perplexed state. You can't assume he will pick up on ques, and may have to be more direct until he gets to know you better.