It was a freak occurrence.
It is very rare for there to be more than the occasional patch of black ice in the UK, so it would be reasonable for a club ride of experienced cyclists to take place at this time of the year.
The risk of a group of riders being in just the wrong place at the wrong time when a driver lost control is extremely low - on that same day, there would hve been thousands of club riders out all over the country with never a newsmaking accident between them.