The photo appears to show the project made from pine.
I'd say you're correct.
I'm worried that pine is too soft for this type of project. In your experience does pine hold up well for something like this?
While pine is soft, it's pretty well suited for projects that infants/toddlers use. These types of projects will see a lot of abuse just because they're used by little humans who have no concept of their own strength or of the value of things and have little spatial awareness. If they bash it around, no big deal, it's just pine.
If you use 2x pine stock, it should hold up just fine. You might have to make a few running repairs occasionally, but that would be expected in just about any toy made for a small child, regardless of the material.
Also, if your friend has wood floors (usually a hardwood like oak), pine won't scratch them as easily since it's much softer.