Yes, it can be used as a verb and CNN used it that way.
Verbification in English is common and the linked Wikipedia article explains there are thousands of them:
Examples of verbification in the English language number in the
thousands, including some of the most common words such as mail and
e-mail, strike, talk, salt, pepper, switch, bed, sleep, ship, train,
stop, drink, cup, lure, mutter, dress, dizzy, divorce, fool, merge, to
be found on virtually every page in the dictionary. Thus,
verbification is by no means confined to slang and has furnished
English with countless new expressions: "access", as in "access the
file", which was previously only a noun, as in "gain access to the
file". Similar mainstream examples include "host", as in "host a
party", and "chair", as in "chair the meeting". Other formations, such
as "gift", are less widespread but nevertheless mainstream.
When a noun like 'bonsai' is used in the linked article, there is no doubt that it is used as a verb as it follows the modal verb must and you should use a verb before the reflexive pronoun themselves to make sense.
The noun 'bonsai' comes from the Japanese noun ' 盆栽 ぼんさい' and it means
a tree or shrub that has been dwarfed, as by pruning the roots and
pinching, and is grown in a pot or other container and trained to
produce a desired shape or effect.
[Dictionary.com]
...Those adjacent must bonsai themselves into what little sittable
space...
could be rephrased to
...those adjacent must cram themselves into what little sittable space...
Related question: “To science the sh*t out of something”
