You know, its entirely possible that Russ is telling the truth. The producer who they auditioned for may have really liked the act. But in determining whether to let Russ proceed to the next step, they most likely did a background check. Even a cursory, criminal history check at the very least. If that is the case, and Russ's criminal conviction for stalking came to light, that and that alone would have been enough for AGT to say nada. Especially in this day and age following the 'me too' movement, a brand like AGT would be very, very careful to ensure that contestants are screened and do not have a past that could disparage the AGT name.
The best thing for AGT to do would be to say that his criminal history made him ineligible.