There was an explanatory note saying that a "technical issue" meant that positive cases from earlier in the week were not recorded at the time, so they were included in Saturday's figure. It was also said that figures for the next few days will also include some cases from earlier in the week.
However, while this may go some way towards explaining any big surge in cases that began yesterday, it seems to me that this means that claims from a couple of days ago that things were levelling off were premature - the rise in infections may not be matching the doomsday scenario outlined by the two scientists in that press briefing nearly a fortnight ago, but new cases are still clearly rising at a high rate.
I'd not been checking the number of cases in Wales every day until recently, so cannot say how yesterday's figure compares with what we were seeing in March and April, but 576 is the highest I've seen by some distance - RCT figures were, as usual the highest, but they've remained fairly steady in the past week while those in other areas have been getting closer to them.