The LSJ gives:
The LSJ revision adds some information, but nothing relevant to this usage. The scholia, referenced by the LSJ, gives this story:dividing the voice, i. e. articulate (cf. Hsch., Sch.11.1.250), “μ. ἄνθρωποι” Il. l.c., Hes.Op.109, etc.; “μ. βροτοί” 11.2.285; “μερόπεσσι λαοῖς” A.Supp.90 (lyr.): hence as Subst., = ἄνθρωποι, Musae.Fr.13 D., A.Ch.1018 (anap.), E.IT1263 (lyr.), A.R.4.536, Call.Fr.418, AP7.563 (Paul. Sil.); a usage satirized by Strato Com., 1.6 sq.
μερόπων ἀνθρώπων: men having the "divided sound," expressing a division from the other animals, which is divided into syllables and having the articulate (jointed) voice, this is the sound [they have].μερόπων ἀνθρώπων: μεμερισμένην τὴν φωνὴν ἐχόντων, ὡς πρὸς συγκρισιν τῶν ἄλλων ζώιων, ὅ ἐστι μεριζομένην εἰς συλλαβὰς καὶ ἔναρθρον ἐχόντων τὴν ὄπα, τουτέστιν τὴν φωνήν.
The above is my translation (please correct). I thought this sounded like the fanciful creation of someone trying to guess the original meaning from the parts, and it looks like Leaf agrees:
The reference to B 285 concerns the children of Μέροψ. Is there any chance that this usage was original, and crept into other parts of the Iliad? Are there any other good suggestions?μερόπων, an epithet of which the real sense was in all probability forgotten in Homeric days, as it is used only in purely stereotyped connexion with ἄνθρωποι (exc. B 285, q.v.) We can only say with confidence that it does not mean "articulate," μερίζοντες τὴν ὄπα, as in so ancient a word the ϝ of ϝόψ would not be neglected. The other derivations which have been proposed are quite problematical.