The first part of the current article is not to the point and misleading.
To mention a clue, if a generator is rated as “X” KVA it as potentially “X” KVA at 0.8 PF
That is it can give as maximum 0.8*X KWATTS, Which is the maximum real power (KW) it can give at a time.
So if your overall P.F. of your installation is 0.8 you can reach the KVA rating of your generator plate as maximum load (taking into acount to stay a 70% of generators rating in average during lifetime of generator), however if your installation is of unity Power Factor for example you can only load 0.8*X KVA or KWATTS (X being the KVA rated power of the generator).
To sum up for 1000KVA rated generator, your maximum load must never be above 800KWATTS. And if you have unity power factor load your maximum load is 800KVA (which is 800KW in this case) if your installation load PF is 0.9 your maximum load can be 800/0.9=889KVA (which is again 800KW but at 0.9 PF)