Drizzt and Artemis are products of a fantasy universe. Their fighting styles are not really comparable to any realistic combat; we do know that people would use a longer sword (though not a longsword as they typically refer to swords used in both hands) paired with a parrying dagger. Using two longer swords, on the other hand, is a pretty unpractical idea when you think about it. More about that particular thought here and here. Drizzt gets a free pass because he is a dark elf in a high fantasy universe, and I seem to remember Salvatore noting that fighting with two long swords simultaneously is a common fighting style among the drow to begin with.

That said, we cannot know for certain what real combat (on the battlefield or in a duel) looked like, but as I have said before, Drizzt is a product of a fantasy universe, and I further suspect that Salvatore's knowledge of actual historical fencing is limited. What we do know from fighting manuals, like the German ones concerning the usage of the longsword (i.e. the two-handed, historical variant) is that many "moves" would consist of both parrying your opponents attack as well as striking, either simultaneously or in short succession.

I'm going to repeat it a final time: Drizzt is a fantasy character, a dark elf and the best swordsman in the Forgotten Realms. He uses a fighting style that would be very impractical in real life. Ultimately, I suppose Salvatore has written after what looks cool to his mind's eye, and I do not blame him, but it is unlikely to be particularly accurate as far as historical combat goes.