It was 100% a catch. At some point you have to end the play when the guy goes out of bounds, or any player could come over and rip a ball out of your hands for an "incomplete" catch. Good call.
My favorite, though, was the over-turned catch by the Steelers when Mike said "There's just not enough evidence to over-turn this call" as we watch conclusive video of the WR losing possession of the ball, then regaining possession with only 1 foot in bounds.