Fixed it to be more precise.
I suppose whether it's an algorithm comes down to which definition you use.
I think the colloquial definition is something which is user-dependant and very complicated.
However, the dictionary definition is "a finite set of unambiguous instructions", which fits my initial usage.
Strangely though, the colloquial definition doesn't fit the dictionary definition, because the YouTube/Twitter/Facebook algorithms are so ambiguous that the people designing them don't really know what they're doing, since they are evolving by themselves.