Taking his statements apart, he is concerned about racism and injustice. In America, as everywhere, those things do exists, and we should do what we can to reduce them. Reading through his further expressions, which include phrases like "dead bodies in the streets," it is clear that he is speaking rather specifically about the purportedly unjustified and disproportionate killing of African-Americans by the police.
He avoids saying that as a categorical condemnation, but what else fits his descriptions? He has adopted the narrative of activists, that there is longstanding police oppression, perhaps worsening, of African-Americans.
Except there isn't, and it's not that hard to show if one looks at the numbers rather than the anecdotes. I think Colin Kaepernick is likely to be well-meaning, has some courage, and wants to use his popularity on behalf of others who have none. Nonetheless what he has done is ultimately damaging, because he prefers not to think too hard. Increasing the cultural belief of African-Americans that the police are against them and want to kill them has a certain self-fulfilling nature. At a minimum, it lessens the chance that they will cooperate with police investigations of crimes in their own neighborhoods, which is the theme of Jill Leovy's Ghettoside. Which means more dead black people.
This is why media bias is important, and not just something that is inconvenient for conservative political candidates. At its worst, it means more innocent dead people.