Based on the key point you provided, it sounds like your crush is definitely interested in you. The fact that he was watching you from a distance, and continued to look even when you noticed, suggests that he is drawn to you and is likely very curious about you. It's a strong indicator that he likes you, especially since he chose to focus his attention on you in a social setting with his friends.
I would rate his level of interest as quite high, possibly an 8 or 9 out of 10. He seems to enjoy observing you and may be looking for opportunities to interact more closely. Keep an eye out for more interactions, as they could give you a clearer picture of his feelings!