what variety? some do only grow to that size?

Are you saying that the plants only got 4 inches tall? Or the pea pods got 4 inches long?

Pea plant seem to range in height from maybe 2 feet to 6 feet tall. I grow sugar snap peas. Last year they got 7 feet tall.

I believe you can plant peas now in zone 5. They don't mind cool weather. I put some pea seeds in the ground around April 6th. Some are about 1 inch tall now. Some are just above the soil. They haven't gotten frozen out yet (thankfully).

If you have just been through that "river in the sky" rain that came through last week, the ground is plenty wet. You should not have to soak the seeds. If you do soak them, just do it for an hour or even less. (I had some bean seeds I washed off last fall, they started to swell withing two minutes. I hope I didn't ruin them.) Enjoy!

Pea varieties are of two types, determinate and indeterminate growth habit. The determinate type are usually shorter and set a number of pods and then quit growing. Under the right conditions the indeterminate varieties grow and produce "forever" or so it seems.

Maybe an animal ate the tops off the plants. Woodchucks will do this.