That's mainly a question of terminology. Corrosion creates eutectics, eutectics melt.
To be honest, Astaneh-Asl's quote is a little perplexing. Adding previous sentences, he said,
"Here, it most likely reached about 1,000 to 1,500 degrees. And that is enough to collapse them, so they collapsed. So the word "melting" should not be used for girders, because there was no melting of girders. I saw melting of girders in World Trade Center."
I've often wondered whether the last sentence was mis-transcribed, and dropped the word "no" from before "melting", because as it stands the quote makes no sense. But of course, for a conspiracy theorist, it's forbidden to question any small excerpt from a quote that seems to support the conspiracy theory, even if it only does so when taken out of context.
Dave