Can someone please remind me again, does kallego know that iruma is a human? Or it's just implied that he does?
It's heavily implied that he knows. When Kalego was going through his wicked phase (somewhere between 317-321), Balam had visited him and they talked about Kalego's brother. Kalego had revealed to Balam that his brother was indeed the one who sent Atori to infiltrate the school, meaning that his brother is now his enemy. Also, Kalego told Balam what his brother said about Iruma:
"Don't approach Iruma anymore. He is a dangerous and despicable thing"
After that, Kalego had asked Balam if Iruma was a human. Due to Kalego's earlier request of Balam not answering anything that Kalego had asked, Balam didn't answer, so Kalego simply said that nothing's changed and that as the guard dog of Babylis, he'll continue to do his job as it's teacher.
There's a few reasons why it's likely that Kalego knows that Iruma is a human:
- Iruma being the sudden grandson of Sullivan certainly puts it to question, especially if Sullivan has no known children. This likely puts it even more at attention when Suillivan was suddenly detained by the border patrol during the Bartora celebration. Now I don't recall if Kalego was made aware of the reason Sullivan was detained, but for someone of Sullivan's rank to be detained as long as he was, it couldn't have been a simple possible crime.
- Kalego being made Iruma's familiar twice, even after breaking the first contract which should forever invalidate any future contract between demon and familiar. That rule that applies between demon and familiar doesn't apply for a human.
- Kalego is possibly aware of his brother's disdain for beings who aren't demons, which would fit with his brother's assessment of Iruma.
- Balam sensei. Kalego is greatly aware of Balam's infatuation with various species, as well as his possible interest in humans. The fact that Balam didn't react to Kalego's question about Iruma possibly being human is nothing short of a miracle... that is assuming that Balam was never aware of it in the first place. But due to Balam's reaction, Kalego could've realized that not only is Iruma a human, but Balam was aware of that fact for a longer time.
There are other reasons along with these, but they all add up to helping Kalego figure out the seemingly inconsistent and logic-defying situations that surround Iruma. And as smart as Kalego is, he could very well put two and two together and arrive at the conclusion, which I'm certain that he did.