Why shouldn’t he cross?
Lots of U.S. citizens cross the border to visit in Mexico, such as tourist destinations or relatives/friends. Nothing in the article indicates he intended on staying on the U.S. side permanently.
You puzzle me.
Visitors from Mexico to the United States who are not US citizens are required to have a visa and a valid Mexican passport, green card or a border crossing card. Many people who live in Juarez have border crossing cards that allow them to enter the U.S. as long as they do not go more than 25 miles into the interior. Visitors to Mexico from the US who remain in border towns can cross the border unimpeded, but if they travel more than 20 kilometers into the interior, they have to go through a Mexican aduana station, present a passport or WHTI-qualifying document, fill out an application and get a permit, which is stamped, and which has to be returned to aduana office when they exit the country. I have no objection to his crossing. I would just like to know what his documentation is.