Comment on XenoRancor by suburbbum

As awsome as this is, I'm kinda wondering how this Xeno came to be. Did a facehugger inplant an embryo into a rancor? But then again that would be a bit tricky seeing as how small the facehugger is campared to the rancor, seeing is how the rancor could just squish or eat the facehugger. Or was this a product of genetic engineering like the mantis alien?