That's a rare use of the phrase. But yes, in this case, it means "physical/tangible". Usually "of substance" means "of importance" or "relevant". For example: "This is a question of substance that deserves closer study." = "This is an important question that deserves closer study." It can also refer to intelligence, often in contrast to something trivial or stupid. For example: "Unlike most rappers, he writes music of substance." = "Unlike most rappers, he writes intelligent music."

Yes, it seems to mean that here. This is an unusual sentence. Usually "of substance" means there's something real about it beyond what a person can see. Or "of substance" can mean it has higher quality. A book of substance makes you think a lot.