I think it's just for the trailer. They used that German techno song as the background for the whole trailer, so maybe having the regular Bruins horn (with the duplicate music to come) wouldn't have worked, so they substituted another team's horn, perhaps.
Just spitballing the idea out there. Personally, I think it's reading a little too much into the game. Then again, if they're wasting money on^D^D^D^D^D^D^D^D changing the Garden's concourse areas, they might be thinking of retooling the horn.
Then again, it was our horn in 2011, wasn't it? Hockey players and fans are superstitious - if they change the horn and we tank, at least one idiot will say it's the horn. Why tinker with it when we've done pretty well - four years, two Stanley Cup finals, one win. When the Chara window shuts, change the horn each year until we find one we like.