Name coined by George Berkeley (1685-1753) for his own philosophy, now more usually called subjective idealism.
Berkeley’s choice of the term was to emphasize his own view that matter does not exist, but in calling his opponents (Rene Descartes (1596-1650), John Locke (1632-1704), and so on) materialists he was using ‘materialist’ in an unusually weak sense.
Descartes and others did indeed accept that matter exists, but they did not deny the existence of other things too, notably souls or spirits.
G Berkeley, A Treatise Concerning the Principles of Human Knowledge (1710)
Boswell says nothing about Johnson’s foot bleeding. He says instead that
After we came out of the church, we stood talking for some time together of Bishop Berkeley’s ingenious sophistry to prove the non-existence of matter, and that every thing in the universe is merely ideal. I observed, that though we are satisfied his doctrine is not true, it is impossible to refute it. I never shall forget the alacrity with which Johnson answered, striking his foot with mighty force against a large stone, till he rebounded from it, ‘I refute it THUS.’