She ignores "good luck message" but initiates convo when in person?

So I sent this girl a thoughtful "good luck with your exam today" message two weeks back. No response.

Then when I see her two weeks later she initiates conversation telling me she passed the exam.

Because it's so late it just doesn't seem sincere. Why would she ignore me and wait to tell me two weeks later?

I was v interested in this girl but this just seems like a red flag to me.
She ignores "good luck message" but initiates convo when in person?
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