Apple ID and Phone Number in use

I think you are probably okay. As a precaution, change your password.

 Apple ID Password Change.      

 What to do after you change your Apple ID or password - Apple Support     I suggest doing this before you change your Apple ID or password.

Also, Check your Apple ID device list (https://support.apple.com/en-us/HT205064) and remove any device that shouldn't be signed in using the steps in the link.

Is this an email you received or a text message about the time you were signing into your MacBook Air? More information would help.