Follow his activity. He is cowardly and not a newbie, but always appears at the moment when it is possible to "peck" someone on the sly. Such people take advantage of the privileges of allowing alternative accounts because they are weak in reality to be cheeky and picky from their "safe-obedient" other accounts.
Why am I not surprised in the least? Guys like this are too cowardly to confront matters with their main accounts and feel it's okay to attack others with the alt so that way nothing gets linked to their original accounts as you pointed out.
As for the matter of having multiple accounts, truth be told it's not an easy feat to maintain all of them because then you'd have to share your time and try to make all of them active especially if they are in different sign campaigns.