It should be noted that the guy did not escape ICE arrest.
A judge has wide discretion in how they run their courtroom. It is in the best interest of Justice if people are not intimidated from coming to court and seeing ICE arresting people outside the doors of a courtroom can cause intimidation. Immigrants may not want to show up for subpoenas or testify if they think they'll get arrested and the Justice system requires people to be willing to come to courts. It's in everyone's best interest that law enforcement not use the courthouse as a lure to arrest people, as people will simply stop showing up for court which hurts everyone.
The judge exercised her discretion and let the man use an alternate exit back into the public area. He was immediately followed into the elevator by a plain clothes ICE officer who alerted the arrest team and they arrested him outside. The judge had the man use the alternate door to prevent his arrest from becoming a spectacle directly outside of her courtroom which could intimidate people.