I suppose that depends on the specifics of the experiment; the brief description above doesn't really make it very clear, and the actual paper is paywalled.
When evaluating individuals, facts about the individual should screen off demographic facts. "Men are physically stronger than women" is a statement about central tendency. But an individual about whom you know they are female and a prize-winning triathlete is probably stronger than an individual about whom you know they're a man who watches 14 hours of TV every day.
Or, let's say that expert nuclear engineers are (for whatever reason) 75% men and 25% women. That means if someone tells you, "X is an expert nuclear engineer", your prior for that person being a man is 3:1. However, if you are in a professional nuclear engineering context and meet an individual woman who is introduced to you as an expert nuclear engineer, you should not assign 3:1 odds that this description is wrong and that really she is an administrative assistant or schoolteacher (or an incompetent nuclear engineer; or, for that matter, a man).
Or even 1:1 odds.
Or, you know, 1:20 odds.
In other experiments on biased behavior in hiring — résumé evaluation and the like — the evaluator is presented with detailed facts about the individual, not just their demographic facts. They have a lot to go on besides the person's gender or race or age or whatever. That's how we can be pretty confident that what's being detected is not accurate reasoning about central tendencies (as in your "men are physically stronger than women") but inaccurate reasoning about individual data points.
This is all true, but doesn't seem relevant. The study description says:
participants were simply asked to rate a particular group
That sounds like rating the group, not individuals. It sounds like being asked about the validity of the stereotype itself. And I'm pretty sure the stereotypes mentioned as examples are in fact true:
a series of stereotypical characteristics, for women were: warm, family-oriented and (less) career-focused
The only question is the magnitude of the true stereotypical difference, and whether people estimate it correctly.
It looks like telling people "everyone is biased" might make people not want to change their behavior to overcome their biases:
The authors suggest that telling participants that everyone is biased makes being biased seem like not much of a big deal. If everyone is doing it, then it's not wrong for me to do it as well. However, it looks like the solution to the problem presented here is to give a little white lie that will prompt people to overcome their biases: