Not true, and well known as not true for ages in the economic field. The primary source of monopolies are government regulations (e.g. patents, exclusive licenses, etc). In fact the words "monopoly" and "patent" started meaning "the government will allow this and only this business to do that thing, and will prosecute whoever tries to compete".

HP only have like 25% of the printer market. Realistic alternatives currently are: Brother, Epson, Kyocera, Ricoh and in some markets NEC. Anyone buying a HP today is asking for it.

What monopoly? You just can buy a printer with refillable ink tanks from several competitors, but also from HP. Then you pay the real price for the printer and the printer heads that need to be replaced occasionally.