Probably an editorial error transferring EG's original notes. In the original published write-up of the FR pantheon in Dragon 054, all four elemental lords had the names of the Melnibonean elemental lords (those you mentioned plus Grome and Katakal) and several beast lords also were from the Melnibonean mythos, such as Haashatak and others (and Pyaray, who in Melnibone is not a beast lord but a chaos god). I'm assuming that EG had used these because they were published in the original printings of the Legends Lore, and they could be published in Dragon Magazine at the time (October 1981) on that basis. I think TSR had lost the license between then and the publication of the OGB.