The picture you shown was not just a simple water cooled CPU rig.
It has a CPU and GPU liquid cooled (and not with water) with dual radiators, and custom made piping.
The cooling block for the GPU looks to be completely custom, which is expensive as is.
Those pipes are not just rubber pipes bought off ebay or unknown third party amazon vendor, those are custom made metal pipes with exact bends with the ends flared for the pipe fittings. This is a professionally built rig, likely done in a full fledged fabrication shop.
As another user stated, they could have easily paid 1500 for the fabrication and powder-coating of the cooling system alone, let alone the cost of the actual PC parts.
To put it into perspective, the linked PC is not...