You've named your Particles to VDB grid 'velocity', but it's not actually a velocity grid...it's still just a density grid...because all that's being extracted from the particles are density values (scalars), not velocity values (vectors).
To import velocity values from particles into a tyFlow VDB setup, you'll want to use a VDB Modify operator.
First, use your Particles to VDB operator to initialize an SDF grid, then add a VDB Modify operator and have it modify the velocity grid (initializing from SDF) and enable "include this flow's particles".
Not being able to initialize a velocity grid from a Particles to VDB operator is a bit counter-intuitive...I'll put that on the todo list.
To import velocity values from particles into a tyFlow VDB setup, you'll want to use a VDB Modify operator.
First, use your Particles to VDB operator to initialize an SDF grid, then add a VDB Modify operator and have it modify the velocity grid (initializing from SDF) and enable "include this flow's particles".
Not being able to initialize a velocity grid from a Particles to VDB operator is a bit counter-intuitive...I'll put that on the todo list.