I mean it in the terms of monolithic process vs. service-oriented architecture, distinct from a distributed vs. centralized operational topology.

FaunaDB and CockroachDB are implemented as monolithic processes and can break encapsulation boundaries for performance reasons. For example, FaunaDB does aggressive predicate pushdown to accelerate intersections and joins, which you cannot do if you have to conform to a key/value interface exclusively. It can also eliminate all network overhead for query data that's local to the processing node.

I understand how that terminology is confusing though...how would you explain it?

I think the use of monolithic here is that CockroachDB is higher level than FoundationDB. The project was not designed to be your do-everything-DB that you layer different systems on, but has a specific goal and is intended to be used directly.