You're a little incorrect, but understandably so; the term "rationalist" refers to "rational thinking", which in turn is a term snatched from Daniel Kahneman's book "Thinking Fast and Slow", which summarizes a great deal of revolutionary findings in the fields of cognitive psychology.

However, I agree- they should have picked another name. "Rationalism" already exists. Furthermore, it's an arrogant name to have- calling your group "rational" implies that anyone who's not in your group is not rational.