My guess is that a rando or someone that knows of him lobbed an insult about him, his family, or his vlogs. He reacted by either hesitating to reply, cursing, flipping the bird, or injected some pace that caught up to him later in the race.
Seth seems like a decent person that is pretty tightly wound and emotional. Nothing wrong with that but, if you are going to be a public figure and make your living being one, then you need to develop a thick skin. It isn't always going to be sunshine and rainbows. Many IG influencers and YouTube celebrities don't account for the fact that they will attract haters along with fans. Look at the LRC forum front page on any given day. The majority of threads celebrate personal failures or slam athletes, entertainers, and companies for the most innocuous things like declaring racism to be wrong. It's all negative energy but that drives clicks and site traffic and, let's face it, more interest than reading through pages of platitudes and well wishes. On the flipside, many social media mavens also love to create controversy to drive traffic or cravenly play peek-a-boo by manipulating people's emotions to trigger purchases. Could this "drama" just be a tease to keep people viewing or "I will reveal what I told True Love in a member exclusive livestream on Saturday. To see it, join at the Butter My Bread level or higher...".
Negative attention is still attention and attention is currency on social platforms.