That sounds like a reasonable theory until you consider stage 1 had rotated around after separation and was free-falling stern first. At +6:39 that object came into view from way below and was passed at high speed by the rocket. It was not possible for it to have been blown off the fuselage by the reentry burn because that didn't happen for another 14 seconds. And it sure didn't fall off and drop out of sight below, only to be caught again and passed. I'm still not convinced we know what this was.