In your specific context I would suspect they did not read the book and did the minimum necessary to get a free backlink.
The one you quote is not even a review as this person is not claiming to have read the book, just "looked" at it. How would anyone be influenced to buy a book based on a one line thank you note for a free book?
You're right it does look that way. That is the most half-baked one so far and won’t be using it now. I am glad you brought this up because it has caused me to look at the persons website and I can tell many of their photos of "customers" are stock photos while their links have got some spammy link directories. I do examine the places I contact but missed this, so there's hindsight for me.
In my first contact email I don't mention a link at all, only mentioning it after they give their feedback. This particular one gave me nothing more once I replied to their initial apparent positive feedback (which may indeed have just been lip service) saying that I would link their review to their website.
Regarding your words "claiming to have read" another positive one includes:
"I looked through the book thoroughly" although doesn't give any info about the book in the rest of the review to prove they read it. I
always ask for a bit more detail such as what they liked about it, I will fine-tune my request to be more diplomatically assertive from now on, I think I may have been too open ended before.
All said, I’d think that shorter reviews can be OK so long as all the reviews aren’t like that as Tally implied earlier. A positive review being short and lacking detail could mean it is somehow disgenuine but it could also mean that the person liked it but aren’t very good at / didn’t bother to articulate details.
It seems as though many (not necessarily here) think that short reviews and ones with no text are fake (personally I think fake reviews come in all forms, short and long).
On websites where customers only need to click for a star rating I tend to get rated, the option is there to add text but they rarely do and if they do it's usually one or two words. I know these are likely to be real reviews because I didn’t post them and they are positive 5 and 4 stars (I know that sounds convenient but if they were negative they could be real also OR from competitors).