Walk INS not permitted for non essential purposes.
Perhaps you friend was lucky.
Noted here:
https://th.usembassy.gov/u-s-citizen-services/acsappointment/
Link specifically states appointment required....
"Appointments are REQUIRED for all non-emergency services and are only made via the website, not by email. Please review the information below, and note that if no appointments are available online, it means we have no appointments available"
(Caps not mine)