Does sound like.
I flushed my old mk3 before. Drained it, took the thermostat out, connected the pipe and stuck a hose woth decent pressure into the raditor for 5 - 10 mins. It would run clear, then the odd bits and bobs of rust would then follow.
To be honest, I doubt you will get rid of it all without getting a new raditor. Beware of using raditor flush though!!!