I don't know why Briggs would say that. Maybe it is a show of support for the scheme Smith runs, in effect saying that he wants to stay in Chicago. That would make since because he led the league in tackles this year.
I am not sure if he has ever played in a 3-4. And we don't have a straight up 3-4 defense like the Steelers, Pats, or Chargers. But judging from those defenses, linebackers thrive in the 3-4. Porter, Bruschi, Vrable, Merriman, and Phillips all thrive under the 3-4. Some of them are considered to be among the best linebackers in the league.
It seems like if Briggs were to stay on the outside of the defense where he currently is in Chicago, he would not only have the opportunity to rack up some tackles, but he might also get more opportunities to rush the passer. He certainly would if he came to Miami based on Capers' scheme last year. But maybe that is what he doesn't like about it. Maybe he doesn't think he is best suited to rush the passer. I don't know because I haven't seen him all that much. But if that were the case, wouldn't he be better suited to playing middle linebacker?