I see that most of the new Cobra irons are strong lofted and in these models, the 7 iron has a loft of 31*. And that is pretty strong compared to a lot of companies' irons, and definitely a lot lower than the lofts of irons made 10+ yrs ago.
There is no magic in shot distance. It is completely explainable in scientific terms because only these things control distance in an iron.
1. The golfer's clubhead speed
2. The loft on the clubhead vs the loft on the previous clubhead and the +/- tolerance of the loft of the clubhead.
3. The face design of the clubhead vs the face design of the previous iron
4. The total weight of the iron vs the total weight of the previous iron
We'll assume that your BIL's clubhead speed hasn't changed since he bought the new Cobras.
So that leaves the other three elements. It is quite possible if your BIL's previous iron set is older, the 7 iron had a loft of say, 35* or so. It is also possible this 7 iron in the new set might be on the minus side of the normal +/- tolerance and could be as low as 30*. A 3, 4 or 5 deg drop in the 7 iron loft would be very big in terms of distance difference.
If the new set is designed with a thin, high strength steel face and the old set was a normal one piece investment cast stainless model, the COR of the heads in the new iron set would be substantially higher. Normal cast irons have a COR in the area of 0.77. Well designed thin face irons can have a COR as high as 0.830. That too can be a VERY substantial difference in the distance.
If the new set is made with lightweight graphite shafts and the old set with steel shafts, the total weight of the new set could be lower by enough to allow your BIL to gain as much as 3 to 4 mph in clubhead speed.
Add these all up and you could see a difference of 20 to 30 yards. Doubtful that it really is 50 yards unless his old 7 iron had a loft of 38* or more.
But the point is there is no "magic" in this, there are no new technologies that only Cobra knows about which could increase distance substantially because all of the scientific elements that relate to shot distance are known and have been used in club design for several years now.