The benchmarks use cstore_fdw which is a columnar store that is accessed via the PostgreSQL foreign data wrapper system.
ICMS is a different implementation of a columnar store for PostgreSQL. I don't know it extremely well but my understanding is that it uses the PostgreSQL shared memory system to allocate memory for a columnar store. This columnar store is not queried via standard SQL commands but rather using a combination of a custom query language and some user defined functions.
