Just introduced a 3 yr old male cat to a 7 mnth old male kitten, weird behaviour?

[HesterMofet11]

So I'm housesitting my Aunt's place for a while. I found her cat as a kitten and gave it to her, about 3 years ago. He is de-sexed and she also has a beagle. I brought my 7 month old kitten over because she's looking after him for me when she gets back. They sniffed each other and the kitten seemed pretty indifferent to him and proceeded to explore. The older cat seemed really anxious, flattened his ears and backed up. He wouldn't go near the kitten and stayed perched on the bench. His hair stood up and he is making a weird, low yowling noise over and over. The kitten is just staring at him and making these dumb squeaky/cooing noises. They aren't going near each other and the older cat seems rather disturbed, while the kitten just seems fascinated.

What does this mean??