People who equivocate deisim with atheism seem to be defining atheism as "no theism". It's a simplistic way of thinking where everything is black and white, everything is true or false.
But it isn't a true or false question; it's multiple choice: theism, deism or atheism - where atheism is defined as "no (theism + deisim)".
Then there are those pesky agnostics who just go on to the next question.