MM
Glad to hear I am not the only bloke still alive who has groundlooped....... IMHO even with your very slippery surfce there was just enough friction to kick off the manoeuvre. I say this 'cos with literally zero friction I guess the normal weathercock stability would have come into play - at least by the time you were drifting at 90 deg! There had to be some small destabilising force from somewhere.
JF