I do believe that this is true but it does seem fishy that he was there. He was found to have, "showed up with multiple IDs, an unlicensed, unregistered vehicle with fake plates and weapons and ammunition" (NBC news). Which does raise a few big red flags. It was also found through ABC News that, "There are indications on social media that he supports Trump and was at the RNC, according to sources.". Which does show that he was supporter which he also said to police and to others via a video released a few days after.
Note:
I did label this misleading because the reasons he was their are misleading but it is true that he did not want to kill the former president.