The Stranger Things intro scene is CGI. Artists were consulted who originally created similar titles in the 80s with practical effects to see how they could do it too. The old-school artists said to just do it in CGI because that’s what they would have done.
I recall Amazon’s Lord of the Rings title sequence [1] received some criticism for looking fake, even though they filmed it practically [2]. I’d guess it was due to folks assuming title sequences are CGI, combined with the fact that few people really know what poured liquid metal is supposed to look like.
There's a similar problem with gunshots and explosions - we want what movies have given us which is not what they actually act/sound like - so much so that live recordings of actual gunfire/explosions is often deemed "fake".