High chance that the account was a sr member rank before and deleted his posts which is uncertain reasons for me.
As I see the account never received or sent any large merit or sending merit to his/er alt accounts, unless proven, thats why merit abuse is not the case here.
Not exactly true. But your first guess should be right. They should have deleted their older posts or the account should have been hacked at the mid of 2018 going by the password change and the email change dates. Also, the account became suddenly active after a long hiatus. Going through the bpip data, they have sent large chunks of merits (5-10) for one liner nonsensical posts. Possibly all those accounts should be his alt accounts. From those lists, some of the accounts have been banned from posting and some are inactive while others are still active.
Interesting all those linked accounts went to inactivity mode at the same month and few of them at the same dates. Another fun fact is that, all the linked accounts have been ranked up to Member rank by receiving exactly 10 merits from various users. Either this should be a chain of alt accounts handled by a single guy probably, not really sure of them.
Possibly connected alt accounts :
1.
Hughes_Ryan2.
alimarh3.
losiva4.
Bolivar_Tony5.
zissmieusP.S You could move this to Reputation, doesn't seem to fit in Meta section.