The better question is: why did my 谁有一万块 show as false? haha

Good question, who knows the answer?

Because only one question word per sentence is needed. 谁 (who) and 吗 (yes/no?) are both question words, so using both would be like saying, "Is there who has ten thousand yuan?"

Source: ever-helpful Chinese boyfriend

I think 吗 is for yes or no questions