It's true. For the first time, man consciously created antimatter in the form of antiprotons at the University of Berkeley back in 1955, their names were Owen Chamberlain and Emilio Segre. Since then, man has learned to create whole atoms from antimatter, it seems to have been done for the first time by Walter Elert and Mario Macri in 1995 at the Fermilab laboratory in Illinois.
In both cases, the method is approximately (very roughly!) the same - a particle accelerator.
If the question is whether antimatter produces a human body, then the question is more complicated, but the answer, oddly enough, is also yes.
wikipedia.org states that the isotope of potassium 40 sometimes (once in a hundred thousand) produces a positron during beta decay. In a human body weighing 70 kilos, about 0.0164 grams of potassium-40, which gives us 4300 decays per second. In total, every 23 seconds a person produces one positron.
I don't think so. In order for antimatter to arise, a certain reaction is needed. And in order for it to pass, either an unstable particle is needed, after the decay of which antimatter would remain, or a reaction of particles at huge energies. But, as you know, electrons, protons and neutrons in the human body are absolutely stable (without going into details), and high energies have nowhere to come from, therefore, a person cannot produce antimatter.