I find these terms strange. I have to pay for the high resolution and SVG but still have to check for right violations.
For a payment of 5$ (compare stock photo prices), I expect the right to use it
At least, that's my understanding of the relevant law (IANAL).
The image element resource licenses are listed in the Resources section. Most of them appear to be relatively permissive licenses though some require attribution.
I get the impression it's a nice little side project, and mostly for fun. I guess he didn't what to go to the expense of purchasing licensing rights for stock images or searching out high quality resources which are in the public domain.