Circuit Analysis of Op-Amp Offset Voltage Tester

I am reading Understanding Op-Amp Parameters section 11-9. I would like to get my work checked.

My assumptions:

• The servo-loop, presumably the op-amp configuration right before V_out, maintains the V_out of DUT at 0V with the virtual earth of -ve input.
• The feedback capacitor (10nF) should effectively open-circuit the feedback of the servo-loop.

With the above, I have worked on a numerical analysis to be this:

$$V_{offset} = \frac{V_{out}}{R_f/R_{os} + 1}$$ $$V_{offset} = \frac{V_{out}}{10K/10 +1} \approx \frac{V_{out}}{1000}$$

I am unsure of my answer, because 10k/10 + 1 is actually 1001, not 1000. It's close but I'd want a very accurate result for this sort of testing circuit? Or perhaps my calculation is wrong somewhere.

Also, if the feedback capacitor is indeed a DC block, what's the point of it?