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Quick answer, no but they will be able to use your account to log in to BTwifi anywhere.
They may be able to get it if they know how BTWifi works and if you have saved your BTID username and password in a browser.
They can go into the browser settings for saved passwords and find your username and password for BT and they would then be able to access your BT accounts and BTWifi
They can use the above for any username and passwords that you have saved in the browser.
Only if there isn't a master password set on the browser.
Which there seldom is.