AITA for assuming the worst about my brother?

TW: Discussion of illegal sexual content

I (28F) need some outside perspective because I’m struggling to figure out whether I’m being paranoid or whether my concerns are legitimate.
My husband (30M) and I opened our home to my younger brother (18M, “Ty”) a few months ago to help him get a better start in adulthood. We both grew up with abuse and neglect, and I’ve always filled more of a maternal role in his life. Because of that, he’s always been very open with me about relationships, sex, mental health, and pretty much anything else. Honestly, he has almost no shame when it comes to discussing that stuff. At Christmas dinner he casually told our entire family what his favorite sex toy was. That’s part of why this situation stands out to me, him being secretive and evasive is very unlike him.
A few months ago at a family birthday party, he admitted while drinking that he had a serious porn addiction and struggled to get off with real people. I tried to give him nonjudgmental advice and didn’t think much of it.
A few weeks later, he told me he’d been scammed out of $50 on Twitter trying to buy a “package.” When I asked what kind, he immediately shut down and said he didn’t want to talk about it. I let it go.
Then a few days ago, he called me because someone on Twitter was blackmailing him. According to him, he’d been talking to someone online, sent nude photos, and was now being threatened. The threat was basically: “Send me money or I’ll tell everyone you were trying to get with children. I’ll post your nudes and ruin your life.”
At first I assumed it was a standard extortion scam and told him to block them.
When I got home, though, something felt off. He was unusually guarded and evasive. Normally he’s very open with me, even when he’s embarrassed. The vibes were weird.
Part of our conversation went like this:
Me: “Are you okay?”
Him: “Yeah. It was just annoying because I bought stuff from them.”
Me: “So you did buy something? What was it?”
Him: “Nothing. I don’t know. I don’t want to talk about it.”
Later I started connecting things in my head, and now I’m wondering if I’m being unfair.
What concerns me:
• He’s admitted to having a severe porn addiction for years.
• I know firsthand that NSFW Twitter can contain extremely disturbing and illegal content if you dig deep enough.
• The blackmail threat feels oddly specific. Why accuse him of trying to talk to children if the goal was simply extortion?
• His behavior throughout this has been far more secretive than normal.
• Someone in my extended social circle was recently arrested for purchasing illegal content through Twitter, so this possibility is already on my radar.
I know suspicion isn’t evidence, and I don’t want to accuse someone I love of something horrific based solely on gut feelings. At the same time, I can’t shake the feeling that something isn’t adding up.

Am I being unreasonable for connecting these dots, or are these legitimate red flags?