"Another article has evidence that the bomb was detonated by remote control, which makes me think someone else triggered the blast at a time when that person though Hinrichs would be in the stadium."
Several theories at this point:
1.) The theory you put forth above is plausible
2.) they were watching and set it off when they saw he didn't get in
3.) He was tinkering with the bomb itself and accidently set it off...4.) He may also have been attempting to remove the bomb from the backpack and affix it to his person.
5.) Maybe he had second thoughts and was trying to disarm it? (not likely given the amount of explosives in his apt. Seems this was not a rash decision.
The fact remains that none of these theories jive with Boren's, his father's or the FBI's public assessments/announcements. Neither does the evidence that a second backpack was found with explosives inside located in the parking garage.
I would add another scenario. He was supposed to be inside by a certain time, but when he couldn't make it, the bomb was detonated at that time anyway. His handlers might not have had him in the light of sight.