All buildings are structures but are all structures buildings?

No, because a structure is something made up of multiple parts, and buildings are not the only thing made up of multiple parts. Structures can be cars, buildings, phones, etc. Hope this helps!

In some jurisdictions, where International Building Code (IBC) applies, a "Building" is defined to include a structure that is USED for support or sheltering any use or occupancy. A "structure" is "anything that is built or constructed", including basically anything made by a person or an animal. A picket fence is a structure, but is not a building. Construction or removal of one may or may not trigger a need for a building permit.