I am unable to find something quotable to back me up. So, I can only offer my personal take. I lived in Austin from 2004 until 2014. Not a Texan by any stretch.
When a member of a group says y'all to the group it is warm.
When an outsider says y'all to a group it can be pejorative.
Compare the following in both senses: "Let's get it together y'all!"
In the first sense, it is a rallying cry. In the second sense, the speaker may think you aren't trying hard enough. There, "y'all" was added only to put some stank on the sentence.
The pejorative may be limited to the end of the sentence.
OOOOOOOh, I know what you mean now! It is an in-group thing.
I experienced a less subtle version of that with my usage of "howdy".
Context: I wasn't born in the US, but was only 4 when we immigrated. For whatever reason young me gravitated toward "howdy" as my greeting. Probably just my young love of westerns; regardless, "howdy" has always been my informal "yo".
Anyway, my first few months in the South, local would ask me if I was making fun of them when I said "Howdy all" / "Howdy guys." Same way I've always said it. Now it was rare, but I would hear locals say "howdy" on occasion without ridicule. Something about my saying it caught a weary eye.
When I'm down South now, I just say "Hi". Weirdly, no one else has ever mentioned it.
I have never thought/heard of it that way? Could you provide some context?