Due to the generic code name, the Numix team have decide not to use the code.desktop icon provided by the VS Code package.
So it's icon is configured as a common text editor by default.
How to fix it?
Ubuntu – How to fix vscode icon in numix icon circle theme
icon-themesnumix
Best Answer
Here's a one liner that will achieve what these guys are saying for you. I've aliased this in bash because I have to execute this every FREAKING time vscode updates...