That is very normal in the US. Race seems to be atop many forms. Just today I had to rewrite a medical history form being used by a canadian government agency (mostly a 'do you suffer fainting spells?' type of form). They had adopted a form obviously written for a US audience and "race/ethnicity:___" came just after middle names. That's just not asked in Canada without a very good medical reason, for which this agency had absolutely none. It was a rush job.

That's pretty typical of a lot of government forms in my experience, for collecting demographic information. While it might be tempting to read more into this, I'm not sure it's justified in this case.

...which is optional? Pretty sure that whole optional section is pure demographic collection popular with many large employers.