Electromagnetic Induction in an expanding current carrying loop: Is it Motional EMF Only? Or Transformer EMF too?

Consider the classic rectangular current-carrying loop: a fixed U-shaped rail and a moving projectile (armature). Current flows, creating a magnetic field. That field interacts with the projectile, the Lorentz force pushes it forward, and the enclosed conductive boundary's magnetic flux changes.

I'm used to the standard generalized view: due to the flux change, motional EMF is produced to resist the motion. I'd usually just apply the simple flux rule and derive: V = -vBL.

But I was doing some review on the fundamentals, and was reminded of Faraday paradoxes and Feynman's lectures and realizing the "flux rule" isn't an absolute fundamental law, I started thinking about the actual physical causes of induction, the fundamental causes coming from Lorentz law and Maxwell's law:

Then, I have two options:

1. Motional EMF (Lorentz force acting on the moving conductor).
2. Transformer EMF (due to a changing magnetic field, dB/dt).

Systems with a self-induced magnetic field like this, I always thought #1 was the sole cause. But recently, I realized #2 might have an influence too?

Which lead me to think about others aspects that are changing, consider the stationary rails... If we apply Biot-Savart's law, as the projectile moves forward, new "dl" elements are constantly being introduced to the active loop.

If I define a stationary point (P) inside the conductive boundary, behind the armature I thought: isn't dB/dt non-zero? Because as the armature moves down the rails, those newly added "dl" elements add more magnetic field strength to (P)? Causing a Transformer EMF?

Fundamentally, I know the moving conductor (#1) is the root cause of the geometry change, but it feels like that's not the full story of the induction? When I think about the magnetic field isn't it changing too?

What are your thoughts? I'd love some insight on this.