What's the difference about First Byte between summary and the first of the request?

Hi
There are two First Byte time,one is in the summary result about the page and another is in the first of the request details. What’s the difference of them? In my opinion, they should be same.
Thanks

The summary TTFB is from the start of navigation until the first byte of HTML for the page is returned and includes DNS, connect, SSL negotiation and any redirects.

At a request level the TTFB is just the time from when the request was sent to the server until a response starts coming back (connection, dns, etc are not included).

Thank you!