Not only were they not real snakes, but they were completely absurd, and no real snake could ever be remotely like them. First, they were too fast. Snakes can strike with remarkable speed, but they can’t move over land/branches very fast. The fastest snake on Earth, the black mamba, is still slower than the average human.
Second, they were too aggressive. Snakes aren’t aggressive. They hunt by either waiting in place to ambush prey, or sneaking up on it. They don’t chase it down. And they don’t attack anything they don’t intend to eat. The slightest negative stress can make most of them lose their appetite.
Snakes don’t throw up their food and then swallow it again. They don’t gulp their food down in seconds. Pythons and boas (anacondas are boas) don’t eat their prey alive - they always kill it first. And one big meal can last a month or more - they simply find a warm place to sit around and digest it.
The snakes in ‘Anaconda’ were CGI monsters designed to play into all the fears and misconceptions people have about snakes and reptiles. It was a horror film, not a documentary.