Normal phalangeal  angulation is between 50º and 60º in fronts, between 45º and 55º in hinds.

How come everything I have learned here at college and through the BHS exam system says the opposite?

I have no idea, but I'd hazard a guess it probably has to do with your instructors using outdated material and/or instructors who are long on theory and short on experience.  Whatever the reason, whoever filled your head with such nonsense was in demonstrable error.

We learned that the front feet should be about 45º and the hinds about 50º.

The notion of any one-size-fits-all, "ideal" phalangeal angulation for either end was disproved before the turn of the 19th Century.

The hinds are supposed to be narrower and longer in foot shape, and slightly more upright in angle.

Close, but no seegar.   Normal weight distribution in light horses varies between 55/45 and 60/40.   The form of fronts is usually slightly larger and much more round than hinds because the primary function of a horse's front end is supportive and a round foot is more efficient in terms of weight bearing than is a pointed foot.  For the same reason, normal front feet in light horses are more upright than hinds - an upright phalangeal lever allows the bony column, instead of the suspensory apparatus, to bear a greater proportion of weight.  Conversely, the hinds normally have a slightly lower angle because their function is primarily propulsive.  Within normal parameters, a hind with angulation that's slightly lower than the fronts will stay on the ground until the energy in the extensors is fully utilized before turning over.  This is more efficient than a hind that turns over prematurely due to overly high angulation and more efficient than one with overly low angulation that causes the foot to stay on the ground after the extensor is extended.

Why this discrepancy? The BHS system is quite an old school, "traditional" system so is this new information supported by research or what?.

There is no discrepancy.  The "BHS system" is fatally flawed with respect to horses' feet.  To avoid further confusion, I suggest you peruse Stashak's, "Adams Lameness in Horses" or Butler's, "Principles of Horseshoeing", which are the standard texts of most veterinary and farriery schools.

I am not trying to start a fight I am just very curious and would like to learn as much as possible about shoeing!.

First, read the literature; next, if you really want to learn a little something about horses' feet and their relationship to efficient movement, whenever you look at a horse, look at its feet first. The more you look, the more you'll learn.