The quote comes from the book Codename Villanelle by Luke Jennings. The full paragraph reads
No one ever visits her here – her professional meetings take place in cafés and public parks,
her sexual liaisons are mostly conducted in hotels – but if they were to do so, the apartment would
bear out her cover story in every detail. In the study, her computer, a top-of-the-range wafer of
stainless steel, is protected by civilian security software that a half-way skilled hacker would quickly
bypass. But a scan of its contents would reveal little more than the details of a successful day-trading
account, and the contents of the filing cabinet are similarly non-committal. There is no music system.
Music, for Villanelle, is at best a pointless irritation and at worst a lethal danger. In silence lies
The author could be using wafer as a simile between computer and wafer, to indicate that the computer was thin. He uses the same word exactly once more in another part of the novel, but that time he makes it clear that the intention is to refer to the shape.
From the Fendi shoulder bag she takes a briquet lighter, a
crumpled blue cotton frock, a pair of wafer-thin sandals and a lingerie-fabric money belt.
Now, in the first quote it is also possible that wafer is being used as a substitute for computer. Instead of repeating the same word inside the same sentence, the author, as good practice recommends, opts to replace it by another word. Instead of simply using a synonym or a more general term he chooses a synecdoche. This is, calling a thing by the name of one of its parts. In this case the part is the silicon slices on which the integrate circuits are printed, called wafers. The same tricks that work in music work in literature. You are expecting a repetition or returning to the tonal, but instead the melody does an appoggiatura.
Is it intentional that the first use doesn't have the -thin? Is the author that sneaky clever? I don't know. Maybe.
Of course, being a literary work and being the two interpretations not contradictory to each other, it is perfectly possible that the intention could be to express both meanings simultaneously. There is no need for the reader to make an exclusive choice between the two.
The author confirmed, though, that