Unwanted location sharing invitation from unknown iCloud ID

• What does “fresh phone” mean?
  • Did you receive it brand new in a factory sealed box from an Apple Store or Authorized Apple Retailer?
  • If not, was the iPhone thoroughly cleansed before you received it? What to do before you sell, give away, or trade in your iPhone or iPad - Apple Support
• Why not simply decline the location sharing invitation? Why does Lockdown Mode seem necessary?

From the iPhone User Guide:

”Lockdown Mode is optional and should be used only if you believe you might be targeted by a highly sophisticated cyberattack, such as by a private company developing state-sponsored mercenary spyware.

Important: Most people are never targeted by attacks of this nature.”