I do not say you should be expert in other technologies but you should be aware of what it is and whats the purpose and whats its characteristics and basics.
when we talk of RDBMS (DBMS) like SQL most of the things are common unlike that for NoSQL has different categories.
Its important to understand the different types of NoSQL and its purpose if you want to learn it.
From wiki (https://en.wikipedia.org/wiki/NoSQL)
- Column: Accumulo, Cassandra, Druid, HBase, Vertica
- Document: Apache CouchDB, Clusterpoint, Couchbase, DocumentDB, HyperDex, Lotus Notes, MarkLogic, MongoDB,OrientDB, Qizx, RethinkDB
- Key-value: Aerospike, Couchbase, Dynamo, FairCom c-treeACE, FoundationDB, HyperDex, MemcacheDB, MUMPS,Oracle NoSQL Database, OrientDB, Redis, Riak, Berkeley DB
- Graph: AllegroGraph, InfiniteGraph, Giraph, MarkLogic, Neo4J, OrientDB, Virtuoso, Stardog
- Multi-model: Alchemy Database, ArangoDB, CortexDB, FoundationDB, MarkLogic, OrientDB
more on NoSQL
A funny picture.
More coming next