Hi Arisa,
No, it isn’t necessarily a sign of interest.
He may have stopped walking and looked at you, then walked away while still looking at you because he thought he recognized you and was trying to determine that as he was looking at you.
A way you can approach him indirectly may be to approach him with a question and while he is answering it, you can try flirting with him lightheartedly to see how he responds to it. If he responds, there may be an opening there for you to move the conversation into more personal topics.