I'm not sure if it's intentional or not, but the only one of your acronyms I'm familiar with is UK. But perhaps that because my answer to your first question would be 'no'.

DPA is the Data Protection Act, a law that governs how PI (Personal Information) can be stored, used and shared.

Why would code written or the interviewer's personal opinion of the candidate be the candidate's personal information?

It's information about an identifiable living individual. (In this context, Personal information is information about a person, not information owned by a person.)

The legal definition of personal information for DPA purposes (https://ico.org.uk/for-organisations/guide-to-data-protectio...) specifically includes "any expression of opinion about the individual and any indication of the intentions of the data controller or any other person in respect of the individual".

Apologies, these are terms anyone in the industry in the UK would be familiar with :-)