Like so many internet videos this does not show what initially happened. We are only seeing the aftermath.
Felony or misdemeanor theft is not pertinent here, but to get it out of the way, I will define it. Third degree felony theft in Utah involves money, goods, or services valued at $1500 or above; at $5000 it becomes a 2nd degree felony. A bicycle can cost $1500 and more at bike stores.
https://answers.justia.com/question/2011/05/29/utah-theft-felony-or-misdemeanor-what-la-18048
Whether or not the theft was a felony or misdemeanor is not pertinent to the man’s action. Based on the information in the article lethal force was allowed in order to prevent a knife attack.
“76-2-402. Force in defense of person -- Forcible felony defined.
(1) (a) A person is justified in threatening or using force against another when and to the extent that the person reasonably believes that force or a threat of force is necessary to defend the person or a third person against another person's imminent use of unlawful force.
(b) A person is justified in using force intended or likely to cause death or serious bodily injury only if the person reasonably believes that force is necessary to prevent death or serious bodily injury to the person or a third person as a result of another person's imminent use of unlawful force, or to prevent the commission of a forcible felony.”
Link Removed
The man was legal and prudent in keeping the gun out.
1 – The young man apparently still had a lethal weapon, the knife, was in range to use it.
2 – He was now confronted by an unpredictable crowd.
Notifying the police as soon as the situation was somewhat stabilized was also prudent.