Once upon a time it was a giant star that rotated once every dozen or two hours. Eventually it ran out of fusible material, and gravity pulled it all in until it became solid neutronium.
Most of the angular momentum stayed with the core, and there you are.
And sufficiently dense that the composition of matter inside is fundamentally different, consisting mainly of neutrons, unstable at ordinary pressure.
The radius of neutron stars is measured in small multiples of the Swarzschild radius for the mass of the star. That is, the radius at which the star would become a black hole.
I highly recommend Dragon's Egg, a hard sci fi novel by Robert L. Forward, as well as its sequel, Starquake, for anyone wanting to expand their mind with a fascinating portrayal of neutron star physics, dealing with the hypothetical possibility of life on their surfaces. The relative physical scales of time, space, velocities and forces are mind-boggling compared to our normal intuition.
Because preservation of angular momentum and gravity plus sub atomic forces and centrifugal force plus mass increases due to relativistic effects balance out roughly there for this star. Much more mass would create a black hole.
Without further inquiry I will assume your answer as correct. That said, I do believe her/his question was more of affordance and less about the particular mechanism. At least that is the way I took. A sort of "How peculiar of a place our universe is to allow such phenomenon."
How can something with twice the mass of the sun spin a thousand times a second. An equator speed of 24% light speed...
The Universe is so strange...