That doesn't mean they were admitting it was slow. On the contrary, they said that it was built with responsiveness and feel in mind, claiming that the actual discernible difference between Chrome opening a page and IE8 opening a page would be negligible. That's their own words, of course, and only the real world can actually judge how fast a browser “feels.” They also reminded the world that IE8 is a beta – and performance could improve as it is developed further.
Even though you could infer all of that information without needing to hear it from Microsoft, it is interesting that they would choose to comment on the Chrome browser at all. Perhaps Microsoft is worried about their market share eroding further.