The Colorado ballot is a computer scan card with numbers on it.
As ou can see, there are no names on the ballot - only numbers.
The card contained a typo where 378 was printed on the 379 slot. But only a complete idiot would not know which circle to mark for 379.
In addition, this error works in Trump's favor. Assuming that 378 is a Cruz delegate while 379 is a Trump delegate, a Cruz voter wouldn't have noticed 379 was missing and may have inadvertently marked the second 378 square, thus casting a vote for the Trump delegate. Yet a Trump voter looking for 379 and not finding it would be alerted to the typo and ask questions to ensure his vote went to the right candidate.