Only the extent that to be human is to be racist: that is, to have an automatically (and usually unconsciously) better impression of those who seem like you and your family or who seems in some non-essential way to be like the person you would like to be or have been taught to look up to.
We can be conditioned to like or dislike someone based on their resemblance to a fictional or mythic image we carry around in our heads. For instance, if the only image we have ever had of Our Lord is a long-haired bearded brunette of vaguely Western European descent, let’s face it, if we see a man who reminds us of that image, we’ll expect him to be a humble and gentle fellow and not a jerk. If there isn’t a black man who could possibly elicit a similar unconscious reaction in us, do we not unconsciously discriminate based on race?
If the teacher was only saying that a white person raised in the US is likely to have been conditioned to disproportionately carry around a positive reaction to whites and a negative reaction to non-whites, then that is something worth pointing out. To call everyone racist when we know that every race has people who were born not knowing what a stranger is, though, who naturally sees everyone as a good person until unequivocally proven otherwise, rightly disposes us to dispute such a blanket characterization.
Having said that, the term “racist” carries a connotation that is the equivalent of saying someone discriminates not just unjustly but willfully and even stubbornly. It is an insult to level that term at an entire group of people based on their race, and not just a little bit ironic, to say the least! Considering those people both white and nonwhite who are naturally friendly, open, positive and harbor no natural discrimination against anyone, the universal statement is plainly false, too. Not as many people are as open as that as they’d characterize themselves to be, but those people are unquestionably out there.