He's lecturing reporters about being too lazy to learn the difference beween deportation and witholding order. One means he has to be deported there's no other option, the other means he can't be deported for some reason. There is no witholding order anymore because the gang he's a member of no longer exists in El Salvador. He's smugly lecturing all of them and then one of the reporters realized what he just said and tried to ask him and Miller realizes he just effed up and ends the whole thing.
The gang they say he is part of is MS13, the Trump boogeyman. The gang the witholding order referred to is Barrio 18. The Trump admin said because El Salvador has destroyed Barrio 18, it no longer is a threat to Abrego Garcia so the witholding order is not valid anymore.
But Miller confused the 2 gangs and said MS 13 doesn't exist in El Salvador.