It looks like this person was provided a provisional ballot. You can tell because of 2 things:

1. The election worker says they'll figure it out later, and they don't know if it will be counted.
2. At the end the provisional ballot appears to go in an envelope and a separate bag instead of the normal ballot box.

Regular ballots are always counted and go into a normal ballot box.

This is not as nefarious as it seems. A provisional ballot gets set aside for higher-up election authorities to figure out, and for candidate campaigns to dispute. There they figure out if the voter was actually allowed to vote or not. It could be that there was an honest mistake in the pollbook which prevented a voter from being able to vote normally on election day, in which case that vote will count. But for someone that's not registered and not a citizen, they'll determine that that voter is ineligible, and the ballot will not count.

Anyone who shows up at a polling place that cannot be given a normal ballot for any reason can be given a provisional ballot. It's a way for election workers to 1) deescalate conflict with the voter, and 2) pass the buck up the chain.

An election worker cannot just tell someone they can't vote, which is the outcome the video poster wanted to see. It doesn't matter if the person is a noncitizen. That opens up liability for possibly denying someone their right to vote. The best they can do is offer a provisional ballot which will get thrown away later for people ineligible to vote.