Not every premade is the best team ever. It is possible to beat premades, especially if they don't coordinate. Besides, that could be their "B" team or a group of PvEers that decided to try out PvP together. Now, if you see those same guys quite a bit in PvP, then maybe they are PvPers, but you can't judge someone from just one match. Technical issues, testing new builds, etc. can make a team much weaker.
And just because you see a premade from the same fleet doesn't mean they are a "PvP Fleet." And your team makeup isn't your standard PUG team, but more a group of members of a few different fleets. I recognize Seb, Lousisya, and I'van as regular PvPers. And I assume the bottom guy on your team was the "other guy."
4 Defiants and 1 Gal-X decloaking on one target can easily kill them and maybe a buddy before they can even respond.