Are hydrogen fuel cells considered to be biofuel?
They're made for the same purpose, but they're very different.
Biofuels are made from plants like corn, algae, grasses, etc.. They are used to make burnable materials like ethanol, which are a direct substitute for gasoline. Thus, if biofuel completely replaced gasoline, you would go to the gas station and fill up your gas just like you would now, but with ethanol, not gasoline.
Hydrogen fuel is made usually through the electrolysis of water. The hydrogen is put in a stable form and placed in a condensed form in a fuel cell, which is used to produce electricity like a battery.
Hydrogen fuel cells and biofuel are both better for air quality, but the processes and applications are totally different. Fuel cells are like alternative batteries, biofuels are just gas substitutes.