How To: outline realistic object.

Hey guys I love this design I found online.
I know how to do use blend modes and overlay the type etc.
The main thing I cant figure out is how they vectorized the steak?
Do you think it was done by hand with the brush tool or do you think it was brought into photoshp and doctored then image traced in illustrator?
If you could help me out that would be appreciated.
Cheers
