It actually does make sense. Not saying you're stupid, but in standard English, if you say it quickly, the two sentences are nearly identical.

They're pretty different in British English, I struggled to figure it out until I started thinking about how it would sound with an American accent.

But in "you sing", "s" is pronounced as "s", not as "z" from "using", right?

I pronounce using with an S unless I'm saying it very slowly