UNI is a token, not a coin and certainly not an altcoin.
coins : https://coinmarketcap.com/coins/
tokens : https://coinmarketcap.com/tokens/
I hope you understand the difference between token projects and altcoin projects / coin projects. Token projects are dependent on one specific blockchain (mostly Ethereum) over which they don't have any direct control and have a centralized single point of failure (high fees), because that blockchain does not scale. Altcoin projects / coin projects each have their own blockchain (over which they have full control), their own fee structure and their own network security.
Ethereum : coin / altcoin
UNI : token