How to identify Post Data is hacked using anti-forgery token

I know how anti-forgery token in ASP.NET MVC works.But still not clear about few scenarios. One I mentioned below.

submit a post request with below information

• cookie token(antiforgerytoken)
• form data(first name & last name)
• form input hidden token(antiforgerytoken)

Before reaching server a hacker modified form data(first name & last name) leaving token info unchanged.

In this scenario, how we can make sure the data submitted securely reached server without any modification

Actually this question is asked by an interviewer. I discussed with my colleagues and I searched in Google too. Since I couldn't find a clarity on this I thought to ask here.

I am not sure if this is a valid question.If yes,any help would be appreciated