Another interpretation: One might think He spoke with him only for the sake of the congregation. Scripture teaches, "saying", He did speak with him also for his own sake.
Reading One Word So the Speech Honors Moses Too
Yalkut Shimoni on Torah 431:2
דָּבָר אַחֵר יָכוֹל לֹא הָיָה מְדַבֵּר עִמּוֹ אֶלָּא לְצֹרֶךְ הַקָּהָל, תַּלְמוּד לוֹמַר "לֵאמֹר" מְדַבֵּר הָיָה עִמּוֹ לְצֹרֶךְ עַצְמוֹ.