I don’t see how they could possibly deny it: It has been clear since day 3 that at least part of the core has melted.
The significance of this particular report at this time from this particular source? Lawyers only know.
TEPCO has had on their “reactor status” pages for several weeks “fuel probably damaged” and figures of 20% to 70% of it depending on reactor. I don’t understand why anyone could say this is “first time they admitted” tripe.
Just people trying to fan the flames a little more, the way I see this story.