First I want to say I am sorry that there was injury in this accident. No one wants these things to happen. It's a shame someone has to live with the consequences. I do a lot of posting on the internet to try to educate people so these things do not happen - reduce the risk, so to speak.
But, allow me to fill in some of the blanks in this case.
There is something in the write up about the tire failing BEFORE the accident. I suspect that means that it was KNOWN the tire had failed but was driven on in spite of this. I suspect this may have been a deciding factor in the jury's decision. (Alternatively, the reporter could have been misreading the fact that the failure had to occur before the accident took place or the tire wasn't the cause of the accident.)
Second, improper repair: Could be a plug, could be merely a patch - it is unspecified. Yes, anything other than a plug/patch combination is considered an improper repair.
Why? Because improper repairs fail more often than proper repairs.
How much more often? The statistics are hard to come by, but based on my past experience, a properly repaired tire fails about twice as often as an unrepaired tire, and an improperly repaired tire fails twice as often as a properly repaired tire.
Let me state this in a different way: Even properly repair tires are more prone to failure, and improperly repaired tires even more than that.
I think that unrepaired tire failures are currently on the order of 1 in 500,000 to 1 million. Considering there are 900 million tires on the road in the US, that means that there would be about 900 to 1,800 tire failures in a year. Please note that this is ONLY tire failures NOT caused by a puncture or a repair or some other outside cause, but DOES include tire failures for which the cause is unknown, but not suspected to have an assignable outside cause. Also please note that vast majority of these tire failures are a) not perceived by the owner, or b) did not cause an accident.
So the numbers are small - and therefore the risk, but this case illustrates that the consequences can be severe.