algo.unionFind() not giving me any clustering on subgraph

I have a database of a user following something like a blog. Given a blog ID number, I know that there is clustering present in that subgraph as seen in the visualization. So I would like to obtain cluster membership for that subgraph. I have used:

CALL algo.unionFind(
  'MATCH (n) RETURN id(n) as id',
  'MATCH (u1:User)-[:FOLLOWS]->(b1:Blog) WHERE b1.blog_id="123" RETURN id(u1) as source, id(b1) 
  as target',

The subgraph should have 91 nodes in it. In this simple case, I would expect to see 1 cluster. However, what I get returned is the entire graph with the community count equal to the number of nodes (1.7M, in this case).

Can someone please help point me to where I am going wrong?