Help with understanding something about a stolen iphone

As long as

• Your phone was logged into your Apple ID, with Find My turned on
• The thieves have not gotten into your phone to disable Find My or log you out of your Apple ID
• You have not removed the phone from the list of devices associated with your Apple ID

the phone will continue to appear on the list of devices associated with your Apple ID. That doesn't mean that the thieves have gotten past the passcode screen of a locked phone.

If you remove your phone from the list of devices associated with your Apple ID, that will clear Activation Lock and let the thieves reset your phone to "make your phone their own."

It is quite possible that the thieves have sold your iPhone to a "chop shop", but I would think the chances of them getting your data from a disassembled phone are rather low.

This may help you --> Do's and Don'ts for lost iPhones - Switch… - Apple Community