Yep, this. While I've never played professionally, I've played plenty of football at the amateur level, and there is no such thing as a tackle where you weren't the least bit reckless but still ended up smashing your studs into the opponent's leg. That's always your fault to some extent. Even if you didn't intend to do it, you went into the tackle in a manner where that was a possible outcome, and that simply isn't allowed. If you take the necessary precautions - i.e. what the rules literally say you must do - then you physically cannot end up stomping on the other player's leg. Anytime that happens, it's because you went into the tackle in a manner where that was a risk, and that's against the rules. It's that simple.
You might accidentally brush your studs across someone's calf if your leg is physically knocked in that direction through the impact of the challenge, but that's a different matter. Anytime you drive your studs into an opponent with force, you did it wrong and it's a foul. It's trivial to tackle in a manner where there's no chance that you end up driving your studs into someone's leg. That can only happen when you're reckless. That's against the rules because it has such a high chance of injuring the other player, and it's entirely avoidable if you care about other players' safety.
The only exception, which happens once in a while, is if you're literally just running and then another player slides in and places his leg where your foot is coming down on your next step, and it's impossible to react fast enough. I've seen red cards given for those (Pogba got one once, I recall), but it shouldn't be a card or even a foul. That's the only time you can sink your studs into a leg and not be at fault.