Scrum Guide tells us to inspect people at retrospectives: http://www.scrumguides.org/scrum-guide.html#events-retro
Inspect how the last Sprint went with regards to people, relationships, process, and tools
The purpose of inspection is later adaptation to what was discovered. But regarding people you can not just say: "John was not performing well during this sprint". You will get a lot of excuses instead of something constructive, which is natural for people.
Needless to say that blaming people in front of other people is not psychologically comfortable.
So what does it mean to "inspect people"?