If you have other Source games mounted (TF2 for example), try unmounting them and then restarting the game. Certain games can override GMod textures due to naming conflicts.

Im pretty sure the texture is from one of the apartments in half life 2

This particular texture exists in HL2 but it's exactly the same as the version that's included with GMod, so that shouldn't be an issue. It's likely being overridden by another game, or maybe an addon you have installed.

To find out where the texture is being loaded from, open the developer console (Shift+Esc) and enter the following commands one line at a time:
After submitting each command, the console should show some green text pointing to the location of the texture/material file. It should contain either hl2_textures.vpk or hl2_misc.vpk, but in your case it'll probably point to another game or addon. Unmounting that game or disabling that addon should fix the issue.