What is meant by 1 kg Biryani?

It depends on how hungry the individuals you're feeding are. A typical Indian adult male consumes between 100 and 150 grams of meat each day, not including the other foods consumed. People with larger appetites can consume up to 250–300g of food. Even if a few people can achieve it, anything beyond is not typical.
The normal meat-to-rice ratio in biryani is 1:1. This is a ratio for home cooking. You can reduce the rice according to how rich you want the biryani to be. For ten people, the expected typical ratio (1:1) is 1.5 kilograms of beef and 1.5 kg of rice. To produce a richer biryani, add 1.5kg of meat to 1.2kg of rice (1:0.8).
Because beef is the more expensive component, restaurants use 0.75:1 or even 0.5:1. Wedding biryani is typically 1:1, but contains considerably more ghee/fat and spice mixes than home or commercial biryani: one  feels fuller sooner, and they can serve more guests with less. That is why Eatsure biryani's are "finger licking delicious.