All I've done with the NCR is briefly talk with them before entering Primm. I made the robot sheriff is that sufficient to make me shunned or is this a glitch?

Hmmm good question, when I made the robot sheriff I didnt get shunned, all I know sorry pal

Have you:

Sided with the Legion
Killed any NCR soldiers
Stolen from then killed NCR troops
Sided with the Powder Gangers

Making the robot sheriff doesn't make them shun you.
Killing them
Stealing from them
Siding againist them
and Being better than them, are all factors that put your Rep down.

Ohh are you wearing Powder Ganger or Legion faction armour?
I assume you don't have BoS faction PA yet .

Siding with the Powder Gangers in Goodsprings will get you Shunned by the NCR.

Unless this was patched in, then no.

I completed Run Goodsprings Run and it gave me a Shunned reputation with the NCR.

I've done that quest at least 5 times now and my NCR rep was always untouched after that quest.

Doesn't say anything on the wiki either.

It probably has something to do with NVEC then. Its an unofficial patch I have and I sometimes forget its on.

weird should be a bug or something?