If you read the full sentence in the article, you will note that it continues by saying that the label is "slandering." Something has to be untrue for it to be slander. Therefore, by saying that labeling people in the crowd as Nazis is slander, it denies that there were Nazis in the crowd.
That employee is taking the position that "there are" is equal to "all those people are", the same flawed logic is being used as a premise by a lot of commenters here.
It's so blatently wrong that it's hard to assume good faith.
Now that you pointed it out I see what you mean, but I wouldn’t call it blatantly wrong. To me the statement honestly read like it’s lumping all protesters together, or at least it’s certainly not making an obvious attempt to differentiate.
> ... or at least it’s certainly not making an obvious attempt to differentiate.
It does not need to.
Yelling "Fire!" in a cinema hall does not need to be accompanied by precise instructions as to where said fire is burning. It's a warning, not a debate.