I actually think this video is a great training point.
One broadly misunderstood aspect of law, by players and referees alike, is the charge from behind. Many people think that if a player was flattened from behind, it must be a foul. But this isn't so.
Let's pretend this wasn't a dive. You have a defender who is running alongside the attacker and not moving towards him, about a yard off. The attacker then steps into him and is the one who causes the contact.
How can you possibly make the argument that the defender has acted carelessly in regards to the collision?
In many cases, if the attacker steps just in front of the defender in a manner in which the defender has no opportunity to avoid the contact, a foul should not be called.
Though in this case, given Vardy's legs tripped up the defender, if it's not a dive it's still a foul against Vardy.