Why did she look at me like this?

I recently ran into my ex and it was very strange especially since we broke up 8 months ago. About a month ago, I was at her work, a movie theater and I was standing waiting for my date to leave the bathroom, and she walked by and I saw her in a mirror. From the moment she turned the corner she was starting at me and kept looking at me in an odd way. She kept staring at me until she went down the hallway.
My friend who was with me dubbed the look as 'i miss you eyes'. She looked at me like she did in the past. And that threw me for a loop.
She's engaged and that didn't make sense in why she looked at me that way.
We broke up because she is a Mormon and I'm not. We struggled with the difference for 5 years. She said she couldn't date me anymore because of the religious stuff and that's when we went out separate ways.
Why did she look at me like this?
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