The -rm commands helped me make sure that no older versions are present on my system
Er, yes; but as the first section of that link says:
If you installed wxWidgets through your distro's packages (rpm, deb, tgz, ebuild...) just uninstall it normally.
You almost certainly had the official Mint wx3.0.4 package installed, so it would have been easier/safer to uninstall it.
The other thing to mention, relevant to debian-based distros in particular, is to use 'update-alternatives' to select which of several installed wx versions is active. To see what's available you'd do:
sudo update-alternatives --display wx-config
To select one of these:
sudo update-alternatives --config wx-config