2K Primer has a very high solid content compared to acrylic primers. you will need to use the hardner when you mix it up -
eg 4 parts primer 1 part hardner 0.5 part reducer/thinner
Basically what the guy was saying is that you can use the 2K primer as a spray putty. eg block/file panels straight + add poly-filler to low-spots,
spray 4 coats of 2K primer, block/file primer, if needed spray more coats of primer then block flat, & you should end up with a nice straight finish.
hope that helps
sam