According to this link:
https://apnews.com/article/us-news-george-floyd-race-and-ethnicity-death-of-george-floyd-2e3c8cb4878b808ddb6886a6fb956fe1
He was asked the following:
"Did you, or someone close to you, participate in any of the demonstrations or marches against police brutality that took place in Minneapolis after George Floyd’s death?” The second asked: “Other than what you have already described above, have you, or anyone close to you, participated in protests about police use of force or police brutality?”"
he was in D.C. to commemorate the 'I have a dream' speech and was wearing an anti-police brutality t-shirt... is that 'participating in a protest'? Probably not... but he ought to have disclosed it really as it is obviously in the spirit of the question.
I do not think it is enough to prejudice the whole trial personally but I don't blame Chauvin's lawyers for basing an appeal on it.. I would if I were them.