The growing list of sanctions against Russia, because of Russian efforts to annex parts of neighbor Ukraine, have hit the Russian arms industry particularly hard because new Russian weapons depend on Western suppliers for some of the high tech components needed. China is taking advantage of this by pointing out that China has become a major producer of high end electronic and mechanical components and can probably replace Western suppliers now unavailable because of the sanctions.
While Russia does not buy a lot of foreign weapons it does buy a lot of high-tech components (especially electronic ones) from the West. A lot of these items are dual use items that China (and other East Asian countries) also manufacture a lot of. China backs Russian efforts to annex parts of Ukraine and is hostile to sanctions (which it has been under for several decades). China believes they can replace enough Western suppliers to Russia to create about a billion dollars a year in additional business for Chinese firms.