magentic field parralel an normal on planes

Hello,given the photo bellow the magnetic field is shown in red circle.
from the manual shown bellow they say:
"Since the magnetic field in Figure 1 is normal to the YZ plane then its tangential component will be zero in the YZ plane."

The magnetic field is in circles, in some section its nornal to YZ plane in some section its not.
Why they say its always normal to the YZ plane?

The diagram is not accurate. It is somewhat confusing.

Consider the current along the Y-axis. Say a straight (linear) conductor carrying some DC current.

This current will be producing a magnetic field. This will be perpendicular to the direction of the current. It will be in circles.

So the magnetic field will be in the XZ plane (direction will be given by the left hand rule).

because the current is along the Y-axis, the magnetic field intersects both X and Z axis perpendicularly. The direction of the magnetic field will always be on this plane. But YZ plane is perpendicular to this plane.

A vector that is lying in a XZ plane will have zero component in a perpendicular direction. YZ plane has no component of the magnetic vector.

I hope you understand now.