This may not be 100% accurate, but the true story between these two goes along the lines of......
A bloke in italy designed it, got it patented, took it to Schluter and they said "That'll never take off" and sent him packing. As soon as his back was turned, Schluter thought "well maybe????" and started to produce it as Ditra Heat.
But after being rejected the little italian fella took his idea to another German company who makes the wires for the Thermonet systems. They bought the idea and got Thermonet to market it as Variopro using the original patent. Following a dispute and a court case or two, Schluter had to change the design of the matting slightly. They had to change something like the shape, height or indent of the noggins that the wire feeds between, just so that the two systems weren't identical.
So although Schluter made it first, the original design belongs to the Thermonet group.