How to interpret avoidance

I ran into a coworker while walking near work on my lunch break. I was texting with someone and smiling while looking at my phone. When I looked up I saw him looking at me and smiling and seemingly happy to see me, but as soon as I looked up he looked away and completely avoided me and avoided eye contact. He could not have tried harder to not look at me at that point. This is someone I have a very casual working relationship with and he always says hi at work, sometimes going out of his way to do so but he's very unpredictable and hard to read. Any input or opinions would be much appreciated!

Sounds like he likes you from that. But it is the one instant you've described. Have you seen him again since? And if so, what's his reaction been since that occasion.

For a while I thought he might be interested because he's usually nice in person and seems to try to linger and when we see each other briefly he'll then find an excuse to email me, etc. But he's in a position of authority and has sent me inappropriately mean emails out of the blue but I think it's because he's under a lot of pressure and loses it. He has a reputation for being mean with staff but apparently some have said that his emails to me were the worst they've seen him be. After the last one he apologized but I ve kept my distance a bit more since then. We never really argued in person though but our encounters are often akward. For example, I'm admittedly often giggly around him and we'll be having what I think is a good conversation but then he'll tell me to stop laughing (this has happened twice), which makes me very uncomfortable. I've heard he was going through a difficult time in his personal life and that's why he's so difficult at work. He travels a lot for work so I don't see him in person that often and he's much nicer with me by email since the last incident. We're both socially akward and he's in a position that would make it somewhat inappropriate for anything to happen between us so even if he were interested I'm not sure he would make the first move. I'm not trying to gage his interest before letting on that I might be interested but he's very hard to read and I guess the whole situation makes everything more complicated. .

Sorry, last paragraph should read I'm trying to gage his interest...

Another thing to mention is that he called me by the wrong name once and felt really bad about it. With the original incident I guess I m wondering if maybe I remind him of someone else and he was embarrassed when he realized it was just me or if he thought I was smiling at him and was embarrassed when he realized I was just looking at my phone.

I don't think he's trying to keep his distance as I definitely get the sense that he looks for excuses to contact me. For example asking for things that I have nothing to do with (people say he's just confused) but he should clearly know who to contact for what. And he does not have a supervisory role in relation to me. But it's definitely a tricky situation which is why I'm trying to be careful and subtle.