This particular change comes about after Google did a somewhat similar gesture earlier in the year, as Google started to integrate tweets into mobile results. Of course, with Twitter striking a deal with Google some time ago, this synergy is not surprising, and neither is it the first time that both of them have collaborated with one another.
In fact, in 2009, both companies signed a deal where tweets would show up in search results, although after the two year expiry date, it was discontinued, as then-Twitter COO Ali Rowghani decided to gain more control over user content. This deal does look to benefit Twitter more than Google, although I am quite sure that Google will never knowingly walk into a deal that will see them end up with nothing either. Judging by Twitter’s slowing growth figures, this might be the shot in the arm that they need so badly.