The US actually has no idea how many warheads China has right now. Not surprising, since China does not disclose anything related to its arsenal.
If you look at their count they add up to exactly the number of warheads on display at the 2019 parade:
DF-41S (16x missiles, 10x MIRV): 160 DF-31A (12x missiles, 1x warhead): 12 DF-5B (12x missiles, 3x MIRV): 36
Total: 208.
This is not even counting the known 48x warheads on SSBNs.
Unless you think that every warhead in China not in a submarine was put on parade or alternatively, delivery vehicles were built without warheads (lol)... Then China has more than 200 warheads.
As for how much more? Impossible to tell. But the floor is 256.
Why does the US military release this report using this count? I have 2 thoughts:
It is trying to justify a first strike nuclear war to the American public by selling the idea that the US can absorb the "small" Chinese retaliation if it acts now.
It is releasing a report simply to say they know something.
Option 1 would be utterly criminal, but doubly so for the American people if they were wrong, either knowingly to deceive or unknowingly due to hubris.