My naive belief is that VC's invest more in companies that they think will succeed (i.e. larger funding rounds).

Is it possible the model is partially latching onto this, meaning their result could actually be just saying "companies that VC's back more are also the one's that succeed", presumably because VC's have some of their own reasonable criteria for doing this.

I didn't see this discussed in the paper, I wonder if it's results would be as strong if they excluded size of funding rounds as an input.