It is abstract in the strict sense, of course. Every science is, as "abstract" simply means "not concrete". All reasoning is by definition abstract in the sense it all reasoning by definition involved concepts, and concepts are by definition abstract.
Numbers, for example, are abstract in the sense that you cannot find concrete numbers walking around or falling off trees or whatever. They're quantities abstracted from concrete particulars.
What the author is concerned with is how mathematics became so abstract.
You have abstractions that bear no apparent relation to concrete reality, at least not according to any direct correspondence. You have degrees of abstraction that generalize various fields of mathematics in a way that are increasingly far removed from concrete reality.
Numbers, for example, are abstract in the sense that you cannot find concrete numbers walking around or falling off trees or whatever. They're quantities abstracted from concrete particulars.
What the author is concerned with is how mathematics became so abstract.
You have abstractions that bear no apparent relation to concrete reality, at least not according to any direct correspondence. You have degrees of abstraction that generalize various fields of mathematics in a way that are increasingly far removed from concrete reality.