"If it was the brakes, wouldn't the FA's have known this...."
Not necessarily. I work at an International Terminal...and every time I get a whiff of burning rubber, I take heed... even though 99.99% of the time, it's simply the smell of burnt rubber from an aircraft that has just landed which has found it's way into the cabin of the aircraft I'm working on. All aircraft burn rubber on landing. It all depends on which way the wind is blowing, whether you will smell it or not.
The FA's are doing the right thing. It always pays to be careful.
Rgds.
Q.