Are custom video IDs possible? Look at the URL!

We’ve always thought that YouTube assigns a 11-character base64 video ID randomly to each upload. However, the video https://www.youtube.com/watch?v=m4Fi_a9QATM by Joeseppi has the ID m4Fi_a9QATM that ends with ATM, which is a 1 in 262 144 chance . The first 6 characters are also kinda sus.

Do you think joeseppi write a script to repeatedly start uploading the video, check the URL and abort if it didn’t contain the three letters? Or found a glitch similar to the one used by bad apple but it’s a QR code that links to this video? Or is it pure luck?

I could not find an official statement on that, and was unable to contact him.