I think it is "vector" taken in the way the author wrote about it / showed illustrations in the article.
For the second sentence, he's right, we could also write (wrongly) an article titled "Functions are Sequences" and (try to) apply what we know about dealing with countable sequences to functions
Vector spaces can have infinite dimension, so the "only" in the first sentence does not belong there.
The second sentence is also odd. How do you define "sequence"? Are there no finite sequences?