They use blockchain as a synonym of "distributed ledger" (which blockchain is not just.) However, a distributed merkle tree is most of the "block and chain" part of the bitcoin paper. Yet, like other people in this thread, I believe Blockchain has come to include distributed consensus or byzantine fault tolerance, proof of work, and public keys as identities. Just because the word itself wasnt defined in the Bitcoin whitepaper, doesnt mean it hasnt been defined after the fact.

They also claim to have used it two years before bitcoin existed.

https://bedrockdb.com/blockchain.html