As Bert re-encounters the party, looking a bit blackened and the worse for wear (I did not ask anyone to make any saving throws for their equipment against lightning, but I think we'll let that go, for reasons that might become evident), he is shocked. "What's happened to you?" he asks, and listens patiently for your answer.
Once that's done, he says to Lukas, "I'm glad to see that you're well, friend." He then agrees you've probably got it right as far as the trap is concerned - and suggests that perhaps the source of the lightning isn't magic, because it did function again a second time. He hasn't a specific answer for an alternative, however. Bert looks at the trap, believes that somehow the electricity is directed from below. He adds that he doesn't believe the trap has been opened in some time - a couple of months, he feels.
As you puzzle this information out, Bert explains about his explorations,
"I haven't much need for any treasure," he says, "So I felt I'd leave you to it. I'm only here for the adventure. And given that you didn't seem too encouraged to take the passage down, I took it upon myself to go alone. About 70 feet down there's a wide passage that's level, but filled with more of the silkweed. There's some kind of harvesting room just beyond, about 50 feet I'd say, with about six tunnels full of the stuff. They must cut it and eat it. I saw a small graveyard, with four big graves in it, minotaur graves I think, and a little hollow where there are two other minotaurs. Beyond the hollow is a large passage that goes down further, but I didn't look there as I thought I'd seen enough. I think the minotaurs were guarding against that downwards passage, they never looked in my direction." He looks solemn. "Those minotaurs are bigger yet that the two we saw here," Bert says. "I'm not sure how they move from down there to up here, but unless we want to meet them, I suggest we get our goods and go. They seemed passive, so I don't think they'll be up anytime soon, but perhaps they have shifts."
All around, the torches on the walls are beginning to run down, suggesting they're changed regularly. You did not see a source for torches, so you don't know where they might be brought from.