I was wondering when you were going to bring this up to meta.
I declined your second flag, for the following reasons:
We can't see downvotes until they reach a certain threshold. In both cases, this user didn't downvote people enough to breach the threshold, so we couldn't see it.
For your first flag, I marked it as helpful, and contacted the community team about it.
For your second flag, you flagged it mere minutes after the first -- which still wouldn't show up because it didn't hit the threshold.
Even though you were relatively certain it was a user revenge downvoting, you could not know for certain. Heck, I can't even know for certain because I can't see anything but patterns of votes.
I've handled this issue in concert with the Community Team.
What to do when you think someone is revenge downvoting
Follow the steps outlined here.
In the future, the best way to handle this is to flag it, but recognize that we don't have the tools to see revenge downvoting until it reaches a certain point, so you may get a declined flag, even if we end up later doing something about it. This is because we have to communicate with the Community team and ask them to look into it, and they aren't always around when we're clearing flags.
No need to flag it more than once once it's marked as helpful.
What I could do better
Not decline the flag, even though no pattern has emerged (and I'm relatively certain the revenge downvote script would pick it up). Mark it as helpful and move on. If there's a case where someone is abusing custom flags to raise their 'helpful' flag count, then I could start declining them.