Well, you're half right - if I'm working a salaried job, my salary isn't going to double overnight just because minimum wage did. The middle class won't see anything out of this except for diminished buying power.
Meanwhile, prices WILL go up quite quickly because the rich aren't going to pay their minimum wage employees more out of their pocket, they'll pass the buck onto the consumers.
It's the oldest trick in the book, stick it to the middle class. Instead of letting the free market function as it should incite class warfare (as your screenshot implied) and when it all crumbles say "Hey, we were trying to do the right thing" (in other words, the road to hell is paved with good intentions).