First you say cam oil blockage, now you're saying the type of tool did it.
 
If i didn't know better, i'd say it looks like that lobe was overtightened and was getting hot every time it was run, causing expansion and the starvation of sufficient lubrication. 
 
You're lucky they are sending you a free camshaft to replace it!

Impact wrenches are very useful, especially for loosening stubborn fasteners, but you should never use an impact wrench to tighten something critical. There is no way of knowing how tight the fastener is unless you check it afterwards with a hand tool, ideally a torque wrench, so what's the point of using the impact wrench in the first place. There's a very good chance of over-tightening a fastener with an impact wrench, which might be what you did (and/or oil starvation factors as mentioned).