Why would that matters? If Americans insist on the nonsensical system that people with no knowledge of the law and plenty of biases should be randomly picked off the street to help decide the law, then a random person they picked off the street to help decide law should be allowed to do so. Its how the weird system of jury duty works. You can't really boot someone from the jury bench for being unqualified or biased when the whole system is supposed to pick people who are unqualified and biased.
Basically the issue is he lied and said he hadn't been to a protest when he had been.
The idea is that you pick those random folks and then the lawyers debate between them and pick the viable jurors out of the larger group of picked people through asking them questions and having them answer truthfully under the penalty of law.
I have done jury duty once and basically they call like 30 people in the courtroom and ask em stuff but only 12 of those folks get picked and if they fill up those 12 spots (which they do one by one as they go and not all at the end) they don't even get to asking all 30 people stuff so if this guy had not lied they could theoretically have swapped him out with someone else that they hadn't gotten to yet which then could have switched up the outcome. In my case I was number 20something so they never even got to me before filling up their 12 folks but the folks that came before me were asked stuff that they had to be truthful about, the case was about drunk driving so like for example there was this one woman who literally thought laws shouldn't apply equitably cause alcohol affects people differently so someone may be more or less debilitated by the same amount of alcohol, and she was debating with the prosecutor about it, so they didn't allow her to be a juror. If she lied about her feelings but then was unmovable in finding the dude innocent because of this opinion then that'd be an issue.