Yugabyte PM here. The goal is to demonstrate that even SQL databases can now be scaled to 1M inserts per second, a feat that was previously reserved for NoSQL databases.
This is not the case. There are in fact many SQL capable databases which showed such results, Clustrix and MySQL Cluster (NDB) among them. Here is link to benchmark (to actually rather old version) https://www.mysql.com/why-mysql/benchmarks/mysql-cluster/