I have a bachelor's in psychology, and after reading this article, I see some red flags right away.
One: Two studies do not news make. This experiment (and variations thereupon) would need to be repeated a solid fifty-plus times by different researchers, using different subjects, in different places, and the collected meta-data would need to be used to draw any kind of conclusion.
Two: Even if a conclusion is drawn, the article should be reporting that the data lends itself to the hypothesis, not that the results are in some way fact. Fortunately, while it seems the researchers are being good and restraining themselves to statements like "this suggests" rather than "this means," whoever wrote the article title and the big bold quote on the right didn't stick to that all-important attitude. Correlation does not causation make, and ruling out confounds in psychological experiments (i.e., getting rid of variables and factors you can't control) is notoriously difficult.
For example, it's well-established that:
(a) People react differently when they're being observed.
(b) People will often try to be "good participants" by doing what they think the researchers want rather than what they would naturally do.
As you can imagine, both of these confounds are pretty difficult to get around, and they can seriously skew your data.
Three: Where's the baseline here? Maybe the actual study goes into this (I didn't read that, only the article), but how is it meaningful to measure all of this without knowing how your participants felt about black people before your study? Did they believe in these stereotypes, consciously or unconsciously? What if for at least some of your participants, their attitude wouldn't have changed at all, or it only changed a little, and you don't know it because you have no baseline?
Four: They only tested white college students, presumably from a single university. Is this university known for being racist? Were these students all first year psychology students? A common problem in psychology is that too many experiments rely on making first year students participate in order to get their participants, thereby skewing the data -- not only are they not drawing from a varied pool, but they're not getting true volunteers. Where and how you obtain your participants can vastly affect your data, and I have to wonder if, for example, we're basically seeing the results of testing the Entitled Snob Man-Children sorority and fraternity.
Five: Why didn't they also test black students??? That seems like a HUGE oversight to me. What about Asian or other ethnicities? Why didn't they also use some baselines such as additional avatar ethnicities or even allowing participants to create their own avatars? A black avatar might've seemed a lot less (or more) stereotypical if they'd created him/her themselves. Did they line up genders between participants and avatars? Did they even use female avatars? How were the avatars dressed? Named? Those things can influence stereotypical perception.
TL

R: Don't worry about this experiment, guys; it needs to be repeated a lot, varied up quite a bit, and done under many different circumstances before it could actually mean anything.