Marx himself considered sole proprietorships to be outside of capitalism. Of course, Twatter Marxoids don't know that.

This video misses an even bigger picture as to why they are hostile to small businesses. Marx considered capitalism to be a progressive force in that it dissolved old social relations he considered to be false consciousness. From the Communist Manifesto:

The bourgeoisie cannot exist without constantly revolutionising the instruments of production, and thereby the relations of production, and with them the whole relations of society. Conservation of the old modes of production in unaltered form, was, on the contrary, the first condition of existence for all earlier industrial classes. Constant revolutionising of production, uninterrupted disturbance of all social conditions, everlasting uncertainty and agitation distinguish the bourgeois epoch from all earlier ones. All fixed, fast-frozen relations, with their train of ancient and venerable prejudices and opinions, are swept away, all new-formed ones become antiquated before they can ossify. All that is solid melts into air, all that is holy is profaned, and man is at last compelled to face with sober senses his real conditions of life, and his relations with his kind.

Basically, this is talking about degeneration due to globalism. Their gripe with small business is that they are more prone to resisting globalism than big ones are, thereby holding up "progress" toward soulless materialism.

Ironically, small business owners aren't even particularly good at that. Lots of them support mass immigration for the cheap labor.