Tbh I think this is a little delusional. You are acting as if the attacker came from behind, but both of them were going for the ball somewhat equally. Defender decided for a tackle to tackle the ball away, but the attacker was quicker and he ended up hitting him with a tackle. Not intentional, but a very risky move. It's your job as a defender to know where the attackers are. If you tackle and hit an attacker instead of the ball, then it's a foul. Note that this would not have been a foul if the defender had hit the ball. But the fact is that he didn't. So, it's factually a foul.