That build just blows my mind. I mean, you shouldn't be getting instagibbed in a FdL anyway, but i've got to see the build now.
Also, the moment you drop out of interdiction, boost boost boost.
I'm still thinking network glitches, but twice is a bit bad. I'm willing to think it may be a cheater with some sort of instant interdiction effect and instant deployment of weapons... but i've never heard of such. At the very least they should have to deploy their weapons.
Doesn't sound like a cheater to me. Still don't know if they had standard or bi-weave shields, or what class. They had a class 2 railgun in a huge class 4 slot! A fully engineered FDL plasma murder boat would turn that basic FDL to dust in seconds. In the heat of battle 5 seconds can feel like 1/2 second, so we only have their word about timings.
I'm guessing no reactive armour and not many HRPs (due to having things like super cruise assist and I bet a fuel scoop too and maybe even a docking computer). A lightweight FDL hull on it's own is paper thin.
My take on this is flying a very poorly specced FDL, using super cruise assist while not paying attention, against a G5 Maxed out plasma boat ganker...this was only going to end in tears.
The other thing to check is your comms panel and look at the Cmdr tab. This will show you all the Cmdrs you have met and at what time. If you killed them, or they killed you, there will be an icon against their cmdr name. This will give you closure of whether it was a human player or not.