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."
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"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."
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"Unlike most rappers, he writes intelligent music."