Anything that has volume or mass is matter.
A testable explanation that is supported or refuted is hypothesis.
This law is a protectionist polity: a policy that is in a way the opposite of fair trade and limits trade and other services across the borders.
The reason is quite simple, this allowed them to monopolize the production and trade of silk and its trade. Because they were able to monopolize its production they could charge whatever price they wanted since they had no competition that would offer lower prices. This made them a lot of money and as they started developing the Silk Road they not only traded silk but several other products and even slaves between Asia and Europe.