What does it mean when a girl hears your conversation with other people?

Why would a girl be listening your conversation if you're not talking to them?

Why would she jump into the conversation and then talk a little bit and eventually leave?

Is she a social anxious girl or a general anxiety girl?

Context:

There's a girl (not sure if she's shy and/or anxious type), she has shown some signs of lip biting, breaking the touch barrier, looking at you from a distance but sometimes she spends her time on the phone.

I was having a conversation with a friend, she has appeared close to us but she was on her phone (probably on Tiktok). Me and my friend are talking about Japanese culture (more specifically, their writing style and how to read their language). Then she suddenly jumps into the conversation saying:"Oh, I confuse the Japanese writing with Chinese, they look alike". I understand what she means because if you put them next to each other (for the untrained eye) it can be easily misinterpreted. Afterwards she kind of stopped, continued with her phone and eventually left.

What does it mean when a girl hears your conversation with other people?
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