Probably. Work hardened 304 will have a weak attraction, as will most 400 series. By the shape of that piece, if it were stainless, I'd have guessed it was a free machining type like 303, which again is usually non-magnetic unless work hardened. If it has the strong attraction of plate steel, it probably isn't stainless.The magnet seems to have the same attraction as a random piece of plate steel. Is that conclusive that it’s not stainless?