I’d think recipes could be had on the web if one looked. Or he might have tried something like mixing gas and stiff grease.
Just type “how to make napalm”, there are many links on “how to”.
Wiki even has an article describing the three variations of US military napalm.
When I was young, some knowledgeable vet described how they made it when he was in Vietnam. As an early teen it stuck in my memory. Never wanted to try making my own, as I found out real young not to mess with gas and flame. You get burned that way!!!!!!