I wonder if that would have been a Newsround newsflash (or more likely left for 10 minutes until Newsround was scheduled to be on air) had it not been the 28th December and the programme wasn't on air?
Anna Home's book about running CBBC in the nineties says that the convention was that breaking news during children's time should be handled by Newsround if it was appropriate, otherwise the newsflash should be on BBC2. The other point I suppose is that there were unlikely to be many adults sitting through CBBC on the off-chance.
There were examples at the time of newsflashes during Saturday morning programmes, the famous one is the Herald of Free Enterprise disaster when not only did Saturday SuperStore start an hour late but there were also a few news updates during the programme, and I remember in the first weekend of the Gulf War they interrupted Going Live for news at ten o'clock. Although there would be a much wider audience around on a Saturday morning, and BBC2 would be doing the OU or not be on air at all. They would often touch on the news as well, you may have seen the Swap Shop that Sir Neil Miles recently uploaded to YouTube where they take some footage of the State Funeral of Anwar Sadat.
The one I always remember is when John Major resigned in 1995, it broke on Newsround and I remember them very gingerly reading it off a bit of paper, and then a minute or so later it got faded out for a proper newsflash.