I can see you have a lot of knowledge regarding this and would be really grateful I could communicate with you via email: admin@cida.site
The Messaging API uses a unique userId that isn't visiable in the app. That can be retreived from a message. If you're thinking about the User ID used to search for a LINE member in the app, no, a bot can not retreive the searchable User ID. I'm happy to help explain further. The terminology they have in the API definately needs improvement.