Unfortunately this is not always true. Company directors invariably get the calculation wrong and buy stock when it's well above it's intrinsic value. Often also the mechanism to boost earnings per share is fiendishly applied to assist management incentive packages, as they are nearly all linked to EPS rather than the intrinsic value of the company or better still the cash generated.
Buy backs also signal that a company can not think of a better way to deploy it's cash to generate an above inflation return on investment. Be careful about buying shares on the back of this procedure.