Any confusion arises because the speed of sound on the string is different in the air than it is on the string.
It is true that if you have a string of 2m in length fixed at the ends, and the wave speed on the string is 2m/s, then the wavelength on the string is 4m (which means that there is a one half wavelength standing wave on the string), and the frequency of the vibration is 2m/s / 4m = 0.5 Hz. That is a very low frequency, too low to hear. Nevertheless, the string would push on the air as it vibrates setting up a sound wave in the air, also at 0.5 Hz. That wave would travel through the air at the speed of sound in the air, which is about 350 m/s, and it would have a very long wavelength in the air of about 350/.5= 700m. But it is too low a frequency for us to hear.
To take a more realistic example with a more realistic speed of sound on a string, consider the lowest pitched string on a violin. It has a length of 0.33m and it is designed to have a mass and tension so that the speed of the wave along the string is about 129 m/s. The wavelength is twice the string length, or 0.66 m. It then vibrates with a pitch of the G below middle C, or 196Hz (that is, 129/.66). As it vibrates, it pushes the air around, and this time the pitch is great enough for us to easily hear. The speed of sound in the air is 350 m/s, the vibration frequency is 196Hz, so the wavelength in the air is about 1.76m.