Posturing and psy-ops. It's likely an inflated figure.

Basically they want people to think they're stronger and that the US is weaker. It's a PR campaign. The US almost certainly has had the same capability for a while and simply had no need to advertise.

Recognize that the US would be foolish to fly a stealth fighter/bomber within range where multiple radar could lock on. They'd start their attack campaigns from far out and pick off the known ground radar installations at the perimeter, along with downing aircraft that tried to intercept them. After that, the US would have air superiority and only have to worry about mobile radar units. In any case, once they turn the radar on to look for the planes, they're broadcasting their location and the plane can just launch a missile down their throat.