AWS makes announcements like these pretty much every 1-4 weeks as-is; they're always innovating - not just releasing for their big conference.

Companies typically do this to spread the media coverage.

Conferences such as reinvent naturally have a lot of touch-points, but it doesn't do well if there's more being pumped out than can be consumed, or so much that your target audience doesn't notice their particular area of interest amongst the noise.

Their event actually "started" around midnight on Sunday with a midnight madness event or something. I think that's when the announcement was made. My wife works in AWS Elemental and stayed up to watch the announcement.