Using central heating radiator or any pipe for AC mains ground is dangerous and even potentially deadly. Don't do it. You can kill yourself or your relatives/neighbor. In case your neighbor have similar ideas of grounding, he can kill yourself. Chances of ground faults in piping are increasing in modern era of plastics (and simple negligence). Either install AC mains electricity for you lab with proper ground or simply live w/o such. You will be fine by connecting all ground terminals of your equipment, supplies and ESD mat/bracelet together without connecting it all to anything. Just learn simp[le rule - when you come to your table in your lab, touch ESD mat first before touching anything else.
Except he isn't using the radiator as an AC mains ground, but an ESD ground, which doesn't have to be perfect, hence the 1M resistor.
At one place I worked, the ESD ground, was just a large piece of copper tape glued to the wall. A few MΩ between the ESD and mains grounds is more than acceptable.
It does have a square within a square on the label.
Even if this voltage isn't a threat to my health, I'd still like it gone because I think it's a threat to my Raspberry Pi and attached electronics which I want to connect via HDMI. I think I can replace the cable and connect the earth to that screw.
Y-capacitors are fairly standard in switched mode power supplies. They ensure the secondary doesn't float at a high frequency, by shunting the capacitively coupled charge across the transformer, back to the primary side.

You could earth the negative side of your Raspberry Pi. If you don't want to do it directly. Connect it to mains earth via a 100nF, 400V capacitor.