Why are there some residual magnetic moment on the zigzag graphene nanoribbon passivated with H atom?

I am considering the relaxation for the following zigzag graphene nanoribbon.

Here the boundary of the zigzag graphene(C: brown) nanoribbon has been passivated with one H atom. I have performed the spin-polarized and spin-unpolarized calculations with VASP. Surprisingly, I found that the spin-polarized calculation gives me lower total energy. Moreover, the total magnetic momentum can be traced back to the C atom passivated with H atom.

Should the zigzag graphene nanoribbon present a spin-polarized ground state? Although the boundary has been passivated. By the way, I have also passivated the boundary with 2 H atoms and then there is net total residual magnetic momentum. Should I use 2 H atoms to passivate the boundary of the zigzag graphene nanoribbon?