Thanks for the report, Qualtagh!
You did the right thing by resigning and I hope you also blacklisted that account. As you may guess from your opponent's name, the user account SlowMo already existed at a time, and did the exact same thing (its now banned, AFAIK). So it's a good guess that the same person was behind it as is behind SlowMoPartTwo.
Banning SlowMoPartTwo will unfortunately only have one effect: There will be a SlowMoPart3, another free account that takes mere minutes to make. Different solutions have been proposed to combat that cycle, but a really good one that doesn't heavily seggregate free and paid accounts hasn't come up yet.