Google Testing Sub (Secondary) Sitelinks
These new sitelinks are sub-sitelinks, secondary levels beyond the sitelink you’d find in the normal search interface.
Sitelinks are designed to help searchers quickly find the section of the website they are trying to navigate toward. It is mostly found for navigational queries but also can be found on other types of queries.
For example, in the image below, you will see a sitelink category for “phones” and when you expand it, it shows categories of phones:–>
We actually covered a year ago in one of those Google update reports that Google mentioned sub-sitelinks then:
“Sub-sitelinks” in expanded sitelinks. [launch codename “thanksgiving”] This improvement digs deeper into megasitelinks by showing sub-sitelinks instead of the normal snippet.
I have personally not been able to replicate this on mobile or desktop.
Postscript: A day later, Google has confirmed the roll out of sub-sitelinks on the Google Search Blog.