It was not in error. President Fox had repeatedly referred to the Minutemen as vigilantes for weeks before they ever took to patrolling the border. He even planned legal action against them before they ever started.
During the joint press conference it was clear what was being asked and that the question referred to the minutemen.
Why all of the jumping through hoops? He called them vigilantes - everyone but you two accept that. Even Secretary of State Rice has called them vigilantes. Here is on of her quotes.
Tenochtitlan, Mexico D.F. - March 11, 2005 - (ACN) The Secretary of State of the USA Condoleezza Rice said, "My country will not tolerate illegal actions by the Minutemen vigilantes" yesterday at a press conference here in Mexico City.
http://www.aztlan.net/condi_vs_minutemen.htm
Note that the date is March 11 - also before the Minutemen ever took the the field.
Again, it is clear to everyone that this administration considers the minutemen vigilantes. Exact quotes have even been given - you're own link to the white house transcript betrays your words.
Bush is held responsible because he is the ONLY person on the planet that is in charge of enforcing the border. He has chosen to not protect the border and even goes as far as encouraging illegal immigration.
You two can't blame congress because the laws are already on the books to protect the border - heck, its even in the constitution but Bush ignores it.