He delegated SP to them for 2 years as part of their sponsorship program. https://steemit.com/steemhunt/@steemhunt/steemhunt-sponsor-program-ends-or-sponsor-report-97

Here are the week’s STEEM rewards and HUNT tokens reserved for sponsors (the STEEM rewards have already been sent to sponsors from @steemhunt.pay). Sponsors get 20% yearly INTEREST (mixed with STEEM/SBD plus HUNT tokens) to his/her delegation support.

They failed to pay him for tokens owed for the delegation. That amounts to theft of services rendered.

Just another justification for ransom.