If you put, correctly, "Crowd of people waiting to see the queen ...", in the caption, your file will turn up in a search for the Queen.
Yesterday I had a hit on 'who me bomb', which according to wikipedia is a type of stink bomb. In the caption, I had "Memorial ... to people who were killed by a bomb ..."; I guess 'me' isn't searched on. NB: who and bomb weren't in the keywords; the caption is accurate, though the search wasn't.
NB: the description isn't searchable, which can help in some circumstances, but in others, the caption has to be as written.
I'm not sure if anyone doesn't write captions, but only descriptions, to avoid that sort of false search.
However, as said above, any keyword can be connected to any other keyword, so you can still get false search results (e.g. you could put red apple, green pear, and that will show hits for green apple), which affect your Alamy Rank/search positioning (though presumably most people will be similarly affected). I see that they have removed the suggestion that "Red apple" "green pear" will stop that from happening. It never did.
OTOH, putting phrases in quotations will hold them together on the file's page, making you not look so stupid, because otherwise their system takes every word and puts them in alphabetical order on the file page, splitting keyword phrases to do so, so e.g. New York not in quotes will be split on the home page, but in any case, the file will show up on a search for York. (try a search on York to check).
It's a nightmare to keyword there, and the implementation leaves much to be desired.