I know that the Community user is not an actual user, and it keeps the site clean. I just wanted to know if there is someone who keeps a check on the actions of the Community user.
Will the rejected edits be manually checked by someone?
Community is no human; things are assigned automatically to Community under certain circumstances, as a result of voting and other actions by actual humans.
Those humans and their actions are accountable, no need to check Community for any irregularities here.
In other words, your edit was rejected by a human, and in this case the human probably clicked the 'Improve' button and marked your edit as 'not helpful'. Another possibility is that there was a conflicting edit that invalidated yours, resulting in an automatic reject.
Such rejection can happen for two reasons I know of:
User manually click "Improve" or "Edit" button when reviewing the suggested edit then untick the "this edit was helpful" checkbox.
Other edit was made to the post and got merged with your suggestion, causing auto rejection. See this question for a good example.