or he could have used a wood element based jutsu to through it off because he does have wood in him and it doesnt make sense why he would use izanagi there
So many years in akatsuki... Itachi would've surely known about tobi's kamui.. He would've put some other jutsu.. Maybe he didn't expect izanagi.. But he knows about izanagi and even the counter to it.. Maybe amaterasu destroyed the sharingan, but his senju dna abilities made him heal it back in time..
He had two ways to get rid of the flames.
He could warp them away to the Kamui dimension since the flames were in direct contact with him or he could use Izanagi and ignore the event.
it couldnt of been izanagi cause the drawback of that is to loose one eye so the best bet is kamui. It didnt slip through him or he wouldnt of been shouting