Hard to say whether or not the guy was using a hack.
I've had extremely bad days where this kind of stuff happened to me as well. I'm not one to scream 'hack' all the time though, so I ususally try to find a reasonable explination.
The other night on my newest profile (http://bf2s.com/player/AH-CiI3r/), there were probably some people that thought I was hacking with my knife. I raked in 5 or 6 knife kills in the period of 2 minutes or so, just because there were people around, and it was open season. When I'm in a knife fight, I'll jump left and right to avoid getting shot, but I most definatly don't hack, since I believe hackers take the fun from a game like this.
The only time I've actually screamed 'hack' across my clans TS server was something that was clearly a health hack of some sort. It was on Gulf of Oman, on a 64 man map. I was running up to take the little village outpost right on the river (the one set back more toward the MEC base). I saw a guy spawn right inside the hut over the water. I ran up, point blank range and unloaded a full clip (and I mean all 12 shots) off of my DAO. The guy didn't flinch, die or anything.
I was pretty pissed, and started screaming 'hack' across my TS, when the guy turns, pulls his pistol on me (he was spec. ops) and pot shot me once in the face. BAM, I'm dead. Best part was, the guy was a member of the clan that ran the server. Needless to say, I made a comment about people/clans that hack, and I was tossed from the server for it.
Anyway, since I know we've all had good and bad days, it's extremely hard to say whether or not he was actually using a hack, but I feel where you're coming from on the sentiment.