Hi, OP!

I suspect your friend's problem is nitrogen, too much of it.

Here's what Southern Exposure Seed Exchange offers about Southern peas: CULTURE: Sow seed 1" deep, 3" to 6" apart in rows 18 to 42" apart. Southern peas have cultural requirements similar to beans. They need full sun and a warm growing season. For best results provide a well-drained soil, with pH in the range of 5.5 to 6.5. Do not apply nitrogen which will result in poor yield and lush foliage.

Now, crowders are in the same category, so maybe the Purplehulls were in a spot higher in nitrogen.

While over fertilization is possible, usually it results in poor pod set. If the pods set and the peas were just small, remember that purple hull is a generic title for several cultivars which have one thing in ,purple hulls. They range from small peas to relatively large ones. It is possible that he got one of the smaller cultivars. When most people say purple hulls they mean one of the pinkeyes

These were Pink-eyed Purplehull BVR peas. Some of the peas filled out to normal size but the majority of them were not normal size. They seemed to have a lot of unused space in the shell, even the dry ones. No seeds were saved from this crop.