Blockchain refers specifically to a linked-list-like data structure which utilizes cryptographic hashes at each node to store an authentication of the tail of t

Blockchain refers specifically to a linked-list-like data structure which utilizes cryptographic hashes at each node to store an authentication of the tail of the list on each head (node). If you have a similar structure using trees, it's a merkle tree. Replication + message signing does not imply either (necessarily).