I'm going to guess that their system was something different at core (like electric) or something very wrong with the set-up.

For yours I guess others have laid it out - the temperature of the water flowing through should be moderate. I've had a mixed system of rads and floor, and quite clearly distinctly different loops and temperature settings (note some rads can be designed for low temperature).

For our radiant flooring, the heated flooring sections are never cold - they move slowly in heat terms, so even if the heat was cut off it would take hours to get to 'cold'.