"USCIS acknowledges exceptions including nonimmigrant categories with dual intent and immigrant categories where only adjustment of status provides a pathway to permanent resident status"

https://www.uscis.gov/sites/default/files/document/memos/PM-...

The literal next line after your quote is:

> While aliens who were inspected and admitted or paroled may request adjustment of status, as a general matter the discretionary approval of such a request is extraordinary given Congress’s intent that aliens should depart once the purpose for which they sought parole or nonimmigrant admission from DHS has been accomplished.