call out vs challenge

call out is not a noun while challenge is a noun.

Word	Noun	Adjective	Verb	Adverb
call out	No	No	Yes	No
challenge	Yes	No	Yes	No

As verbs, challenge is a hypernym of call out; that is, challenge is a word with a broader meaning than call out:

call out (noun)	challenge (noun)
	a call to engage in a contest or fight
	questioning a statement and demanding an explanation
	a formal objection to the selection of a particular person as a juror
	a demand by a sentry for a password or identification
	a demanding or stimulating situation

call out (verb)	challenge (verb)
call out loudly, as of names or numbers	issue a challenge to
utter aloud; often with surprise, horror, or joy	take exception to
challenge to a duel	raise a formal objection in a court of law
	ask for identification