Navid Benders The project by him that enables this is open source (github.com/platformatic/php-node). He also made a real effort to contribute to ext-php-rs with some changes already merged.
So from my perspective everything is fine.
What he does with his product is his decision. While I would certainly prefer it to be open I cant fault him for charging here. Nearly every company uses open source projects and he did more than most by A) open sourcing this functionality and B) contributing back.
That beeing said I did not look into the product, nor the pricing structure, as it doesn't really matter from what I see and mentioned above.