“by someone” at the end of talk.

[blwings]

“She really put her foot in it now.”
“Her and the rest of that bunch, by Roland.”

This conversation is from The Intuitionist by Colson Whitehead.

The name Roland appeared out of nowhere here and I can’t understand what Roland has to do with here. How can I interpret “by” here?

 

[5jj]

My guess is that it could be a euphemistic form of 'by God'.