dialectical materialism is the theoretical framework that marxists use to explain history, economics, social organization etc.
Dialectical means "in a dialogue" (like new vs. old, rich vs. poor, opressed vs. opressor).
Materalism means that everything follows real, existing things and their value (maybe you're familiar with the term material conditions), which sounds completely obvious, but most philosophy before marx was completely estranged from reality in that sense.
Probably not really deductible from the screenshots/it's just goofing around, besides that however, he also made a video about Schostakowitsch where he talkes about soviet and russian history and does the default anti-communism + historical revisionism on Stalin and the SU. I guess you can't really expect anything better from a YouTuber
Bjarne Stroustrup in shambles rn