Kyran never dreamed that the first human he proactively absorbed would be Gael. To be honest, he could not remember all the things he absorbed before. He did not even know what would happen when he absorbed things, especially living things— at least, not after he discovered Bas's and Iss's presence inside the fissure.
From there Kyran surmised that all living things he absorbed would likely end up becoming his loyal subjects. He would then gain affinity to their innate magic.
Gaining affinity to other magic did not require for him to absorb a living thing. He could also absorb concentrated magic energies of particular magic to gain such affinity. These explains why back in the Tower of Tribulations, when he was presented magic paths, there were several magic types he was unaware of.