What Uhrrr is saying is that prob(Person is an engineer | Named Jack and has Jack's description and initial 30/70 ratio) > prob(Person is an engineer | 30/70 ratio)=30%. I think the article goofed on that question too. I'd rather have seen an illustration of the conjunction bias, which is similar. Given Jack's description, what's more probable: Jack is a lawyer, or Jack is a lawyer who likes classical music. (The first one, but people overwhelmingly pick the second one.)