I haven't read the article yet, but surely they can't be juxtaposing waterfall as the alternative to agile. The modern alternative, especially in small to medium businesses, would be kanban.
Ehhhh...Kanban is much older than Agile even if they tried to subsume it and say it's an agile technique, so that's sort of right. But kanban vs "scrum" - which virtually everyone means when they say "agile" - is fair.
Within my company there is a mix of Scrum and Kanban, so Agile != Scrum.
I don't think it makes much sense to say "We are switching from Agile to Kanban", but "We are switching from Scrum to Kanban" does make sense (at least to me)