How compelling is the hypothesis that dinosaurs were killed by toxic plants?
Things in the paper that strike me as suspicious
Associating toxic plant defenses with the Cretaceous

Although there continues to be uncertainty about precisely when plants
first evolved toxic defenses, this period of angiosperm proliferation
would seem to be a strong candidate case. (pg 50)

Against this Gleadow and Moller (2014) discuss Cyanogenic glycosides (CNglcs), a class of organic compounds that can kill overgrazing herbivores from cyanide poisoning,

CNglcs are unusually widespread in the plant kingdom. They are found
in the oldest of terrestrial plants (the ferns) and in gymnosperms and
angiosperms.

Similarly, poisonous terpanoids are found in the Ginkgo; Proanthocyanidins, of which oak or wine tannins are a member, is found also in maritime pines; etc. There doesn't appear to be a strong link between angiosperms and chemical defenses against herbivory in plants.
Claiming that the angiosperm proliferations and extinction of dinosaurs are linked in time

The relative co-occurrence of angiosperm proliferation and the
disappearance of the dinosaurs has not gone completely unnoticed.(pg 50)

The diversification of angiosperms occurred starting about 112 MYa for the Monocots, and 100 MYa for the Eudicots, according to De Bodt, et all (2005). From Figure 1 of that linked paper, we can see that both branches of the Angiosperms were approaching their modern diversity by 90 MYa; a time still 25 million years before the extinction of the dinosaurs. 25 million years ago, our nearest ancestor hadn't diverged from the line that would lead to Old World Monkeys, and was probably arboreal. Evolution can do a lot in such a time. Calling these two events linked in time is suspicious, at best.
Using crocodilians as a test case for taste aversion

Since crocodilians are descendent from the same creatures that gave
rise to dinosaurs, this creates the opportunity to evaluate the
tenability of the proposition that dinosaurs went extinct due to an
inherent inability to learn to avoid eating toxic plants.

Reptilian cladistics are far from settled, but I would suggest that crocodilians diverged from dinosaurs by at least the early Triassic. They are almost certainly more divergent from all dinosaurs than birds. Here is what the authors have to say about birds.

However, in contrast to caimans, birds are in fact capable of forming
learned food aversions. (pg 51)

That seems to really undermine the argument here.