Notably as well, this is more equivalent to a former housemate taking something of yours as they leave, instead of a burglary. The phrase "hacking back" in the title implied to me that an outsider hacked their servers. Not that hacking back would be ethical either way, but I felt misled.

And in both cases, unless you are much better connected than the other person, the person doing the taking will de facto come out on top, by design.

Especially when:

1) The "revenge" crime involves intruding upon accounts maintained by third parties -- in this case, cell carriers, Google, and Dropbox.

2) The theft of IP was suspected, not proven, and accessing those accounts would, at best, only confirm that it had occurred.

Indeed. It sounds like he got a just result for his actions.