The Result here isn't deterministic, sometimes it returns "vec:4" instead of "vec:1".
My suggestion is to change vec:4
to: db.HashSet("vec:5", "vector", (new float[] { 5f, 5f, 5f, 5f }).SelectMany(BitConverter.GetBytes).ToArray());
Secondly, in this code section (and other code sections in this file) I think you should delete the indentation, it looks less good that way.
I mean to change this:
db.HashSet("vec:1", "vector", (new float[] { 1f, 1f, 1f, 1f }).SelectMany(BitConverter.GetBytes).ToArray());
db.HashSet("vec:2", "vector", (new float[] { 2f, 2f, 2f, 2f }).SelectMany(BitConverter.GetBytes).ToArray());
db.HashSet("vec:3", "vector", (new float[] { 3f, 3f, 3f, 3f }).SelectMany(BitConverter.GetBytes).ToArray());
db.HashSet("vec:5", "vector", (new float[] { 5f, 5f, 5f, 5f }).SelectMany(BitConverter.GetBytes).ToArray());
to this:
db.HashSet("vec:1", "vector", (new float[] { 1f, 1f, 1f, 1f }).SelectMany(BitConverter.GetBytes).ToArray());
db.HashSet("vec:2", "vector", (new float[] { 2f, 2f, 2f, 2f }).SelectMany(BitConverter.GetBytes).ToArray());
db.HashSet("vec:3", "vector", (new float[] { 3f, 3f, 3f, 3f }).SelectMany(BitConverter.GetBytes).ToArray());
db.HashSet("vec:5", "vector", (new float[] { 5f, 5f, 5f, 5f }).SelectMany(BitConverter.GetBytes).ToArray());