lost mode in find my iphone

Dear Sir/Madam,

My phone being steal last week.Immediately, I turned on Lost Mode in Find my iPhone apps and click the remote erase button via my iPad. All these while, the lost device are shown in that apps but all in sudden it gone after I signed in the Apple ID in my new phone yesterday and the lost device was replaced by my new phone.

My question is: does it mean the activation lock already turned off and other user can use my phone?

Thanks.