Why does it mention that this was before Haktaras ha'Chelev?
Radak: Also this was evil. They ate it before Haktarah. The Torah entitled them to receive from Hashem's table only after Zerikas Dam and Haktarah! Midrash Shmuel 6:1 - Hashem said, why do you eat the remainder of Menachos, and leave the Kometz (which must be burned on the Mizbe'ach) for flies? Why do you eat the meat, and leave the Chelev in the sun? 1 The Yisrael said, the Kohen will do Zerikah and Haktarah, and afterwards take. The Kohen said, I will not do Zerikah or Haktarah. Give meat for the Kohen to roast. If not, I will take it by force!
Malbim: This was unlike [even] Mishpat ha'Kohanim (a law they established for themselves, unlike Torah law).
It does not say that the Chelev rotted. Perhaps the miracle that Kodesh meat never rotted (Avos 5:5) applied even here. A fly was never seen where they cooked meat of Korbanos (ibid). This is not where they left the Kometz. (PF)
Why did he say "give meat"?
Malbim: You will profit doubly through this. (a) You will give like you want. This is less than the fork would take! (b) If I would take from the pot, you must toil to cook everything, and add salt and spices (for what I will take).
Above (verses 13-14) it says that they took from cooking meat!
Radak #1: He would say that he will take only raw meat, to roast it, and afterwards he would take also cooked.
Radak #2: Sometimes he would take only cooked, and sometimes he would take only raw.
