Sounds like it was pinned back then after the roots were taken out I'd imagine, surveyor wont be taking any chances and will want a survey done for peace of mind as it's 13 years ago since it was done and depends on the length of guarantee, usually about 12 years. Cant understand about the insurer thing unless they think there is a problem or have an agreement with them lol. Just get a structural boy in to make sure, saves hassle