Chemical properties: Sodium metal and sodium amide ($\ce{NaNH2}$ ) are strong bases. They react with ethyne to form sodium acetylide with the liberation of hydrogen gas.
How can a metal considered a base (that too strong)? To act as base it should either donate a pair of electrons (in this case it's single electron) or accept proton or give $\ce{OH-}$ ion but here it's not qualifying any one. So is that statement wrong?
Formation of monosodium ethynide: $$\ce{HC#CH + Na -> HC#C^-Na+ + 1/2H2}\tag{13.59}$$
Formation of disodium ethynide: $$\ce{HC#C^-Na+ + Na -> Na+C^{-} #C^-Na+ + 1/2H2}\tag{13.60}$$
Source: NCERT 11, Hydrocarbons, Page 386