No. "Nah" and "no" meanthe samething. "Nah" is often followed by "man." As in "nah, man."
-Person 1: Do you wanna go to the movie theater?
-Person 2: Nah.
OR
-Person 1: Do you want to go strip in front of my neighbor's house?
-Person 2: Nah, man. That's just gross.
"NAH" is quite similar to "BRO" which is used in the same scenario.
"NAH" Is sometimes followed up by "That's Crazy".
Person 1: Look at this.
*Sends video of something suprising*
Person 2: NAHHH
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Person 1: Look at this.
*Sends video of something suprising*
Person 2: NAH THATS CRAZY BRO