Too bad how in the SSB4 Direct we could see Diddy Kong's Brawl Icon instead of his SSB4 one during the Little Mac segment. :|
The Icon was likely a placeholder until they finished Diddy Kong's official render for Smash 4 since the model would obviously be created first..it was likely that they hadn't swapped out the icon for Diddy to the official one yet.
No it wasn't.
Various voices and animations are reused from Brawl.
Also, Sakurai said "Brawl was made from scratch" even though various voices and animations were also reused from Melee in Brawl just like they are now.
Heck, things from 64 were reused in Melee as well.
Just because they re-used things doesn't mean they were part of carried over code. After all, several things from completely unrelated game were brought into Super Smash Bros. Brawl as well, such as a lot of the trophy models having 'extra' bits from the games they originated from.
Animations are of course going to be re-created if they are re-creating the characters with minimal differences.
Also, voices and sounds get re-used alot. Mario & Luigi's voices in Super Smash Bros. and Super Smash Bros. Melee were re-using samples from Super Mario 64, just with Luigi's voice being sped up and higher pitched to be difference.
Just because Animations are the same and sounds are re-used doesn't mean they are carried over..at least not in regards to how that person meant as 'carried over', IE: Altering the code of a previous game.
All we know is that they likely have the assets from Brawl to use for reference similar to how they had the assets from Melee to use as reference as well.
What you should have said was that there were Melee trophies found in Brawl's code, though some were miscoloured like Donkey Kong Jr, but they could have been put into the game purely to text Trophy Systems prior to actually creating any actual trophies.