From watching the video you shared, it seems like that's how ICE got to him. Apparently he was involved in a dismissed self-defense case that was not a felony. It's important to note that a dismissal does NOT erase the offense from your criminal record, but it does change your record to show that the conviction was dismissed.

This video does not explained if he expunged his records. "Expunged" is not exactly the same as "dismissed" in legal terms. While a dismissal means a case is closed with no finding of guilt, an expungement goes further by essentially erasing a criminal record from public view, making it appear as if the crime never happened, so it won't show up on a background check. Expungement is a more complete removal of a criminal record than a dismissal.

Although expunged records are removed from public records and sealed records are confidential, they usually don't show up on background checks.

However, there are some exceptions.

Expunged records

Public record: Expunged records are removed from public records.

Fingerprinting: Expunged records may show up on fingerprinting background checks because they are run through a federal database.

Employers: Most employers use name-based background checks and won't be able to find expunged records.

Sealed records

Background checks: Sealed records usually don't show up on background checks, unless the requester is law enforcement.

Level 2 background checks: Sealed records may be visible for certain jobs that require a higher level of scrutiny, like federal positions.

Law enforcement: Sealed records may show up on background checks for law enforcement.

Gun licenses: Sealed records may show up on background checks for gun licenses.

If you had your case dismissed and expunged and sealed your records then you are fine, but if you just had your case dismissed and you did not do an expungement to your records, there is a possibility that ICE can obtain your records if they wanted to.

This video is a good example that a dismissal, does not erase the offense from your criminal record.