Why so small?

I have seedlings from an open pollinated Gen. Jack last year growing this year. Nearly all conform to Gen Jack’s behaviors and looks. I joked that all the seedlings had to be self-seeded because the only thing I had blooming at the same time last year when I protected the Gen. Jack hip with the intention of collecting seeds in the fall was American Pillar. Now, I have a small not over twelve inch plant that blooms repeatedly in the colors of American Pillar (dark pink outer petal with pronounced white eye centers). The GJ features are sepals, leaves, and a silverish pink reverse to the petal. The bloom shape is cupped with the center staying open throughout the bloom life very much like Reine Victoria without any small petals inverting toward the center. The petal count stays around fifty to fifty four. I think American Pillar is a triploid and Gen. Jack a tetraploid so the success of AP as the pollen parent seems unlikely. I remember someone else having an AP cross that seemed unlikely. Is AP unusual enough to have crossed ploidys to make this rose? Where did the dwarf size of the seedling come from?

There are many triploids that are fertile: Muriel, New Dawn. And there’s been roses whose sterile parent has given some fertility: Mermaid. I wouldn’t rule out that American Pilar is all sterile, but I have no experiance with it. But I wouldn’t rule out that it isn’t fertile.