Inductive effect in carbanions
The charge on CH2- doesn't say it's electronegative. The direction of inductive effect is from a negatively charged atom to the rest of the uncharged molecule (if there's only one negatively charged atom in a given (canonical) structure) and the effect decreases as we go away from the negative charge. The electronegativity of carbon atoms in organic molecules is more closely related to their hybridization; sp-hybridized carbons are  the most electronegative, followed by sp2- and sp3- hybridized carbons. Thus, your textbook is right.