Sereno wasn't up to date on other issues of case. (Hadn't listed to the 911 tapes.
He was “playing good cop” and leading witnesses on to see if they would reveal more information. Would be the first time a white lie or innuendo was used to try to get more information.
I did wonder if he had heard the Zimmerman / dispatch recording. If so, how did he fit that into the two contact scenario.