From Wikipedia: Shellac is a natural bioadhesive polymer and is chemically similar to synthetic polymers, and thus can be considered a natural form of plastic. It can be turned into a moulding compound when mixed with wood flour and moulded under heat and pressure methods, so it can also be classified as thermoplastic.

One issue of note in this description is that the finished product when using shellac base is a very early thermoplastic with the characteristics of thermoset plastic, being brittle and not easily melted. Once a thermoset polymer is cured, it cannot be re-melted or reformed, but will burn. So bakelite, epoxy, hard rubber, molded shellac, gutta-percha, etc. all fall into the same general family of polymers. Bakelite was the world's first fully synthetic plastic invented in New York in 1907, so all that were used before fell into a closely related family of natural polymers.

So it is not the characteristics of the material, but the source of the basic compound that is in question. Gutta=percha is a thermoset plastic also made of organic natural compounds. The author was wrong in the characterization that shellac is not a molded plastic, because where used in durable products like records, cases, and appliances it was formed the same way as gutta-percha, heat and pressure molded to "set" the polymer into a product shape. Wood flour was the additive that gave shellac the strength to become a durable product.

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Gary
SWCA 2515