(i) In both of these stories, the title character is transported to the past by accident.
(ii) In both stories, the traveler is presented as seen by inhabitants of the period to which he has been sent.
(iii) Both stories address the question of how a modern person would be able to cope if transported to the past.
(i) The Little Monster is sent from and returns to a period where time travel technology is in regular use whereas The Man Who Came Early was struck by lightning.
(ii) "The Little Monster" alternates between the time traveler's point of view and that of an inhabitant of the Pliocene. (In fact, the title is ironic because each perceives the other as both little and monstrous.)
(iii) The Little Monster uses a knife and Scouting skills to survive whereas the Man Who Came Early, lacking necessary knowledge and skills, does not survive.
Thus, Poul Anderson not only addresses a question raised by earlier sf writers, Twain and de Camp, but also presents alternative answers to it.