Why do folks say that Huawei is an arm of the Chinese government?
Because it is. China is a communist country.
"a theory or system of social organization in which all property is owned by the community"
The community is represented by a non-elected government. In other words, the government owns every business and all land / buildings in China.
eg, the chinese government recently seized the Anbang insurance company. Every chinese company has a government oversight department.