This is not something new. Often, when descriptive text is not found on the page to fully match the actual query requested, Google uses the meta description on the results page, unless there is a dmoz description to use. This is no way indicates (and testing does not indicate it either) that Google uses the meta description to determine placement in the SERPS.
It is a mute point though. Since SOME search engines still use the meta description tag to some extent (however minor) then you are likely using the tag anyway, so it doesn't truly matter why.
