AlliedModders - Is this a DDoS attack of somekind?

Every few minutes I am seeing the following spam in my HLSW:

Code:

21:58:15 Traffic from [removed]:50626 was blocked for exceeding rate limits

21:58:15 Traffic from [removed]:50628 was blocked for exceeding rate limits

21:58:15 Traffic from [removed]:50627 was blocked for exceeding rate limits

21:58:15 Traffic from [removed]:50629 was blocked for exceeding rate limits

21:58:15 Traffic from [removed]:50630 was blocked for exceeding rate limits

21:58:15 Traffic from [removed]:50631 was blocked for exceeding rate limits

21:58:15 Traffic from [removed]:50622 was blocked for exceeding rate limits

21:58:15 Traffic from [removed]:50623 was blocked for exceeding rate limits

21:58:15 Traffic from [removed]:50625 was blocked for exceeding rate limits

21:58:15 Traffic from [removed]:50624 was blocked for exceeding rate limits

The IP (which I have removed) is the same, but the port number changes each time. As you can see they are roughly sequential, and this has been going on for around 40 minutes at this point. It's only happening to one of my 7 servers, even though all 7 servers used the same IP, each with a different port. And most importantly, it's not actually effecting the any of the servers ping or performance.

Using the IP address, I searched my servers logs managed to match it to a Steam account. I have banned both that SteamID and IP address in Sourcebans, though I am still seeing this spam after banning both.

In any case, can anyone possibly explain what is (or might be) happening?