I really wouldn't take it to heart, I more think it is a reflections that time has caught up with them about having the right type of conversations, after all they have the books. I certainly wouldn't read too much into culture differences, more parenting styles.
DD 10 and I had very direct conversations about periods about 18 months ago. I'd always been open about it and we had read age appropriate books that she has in her room, but as someone has mentioned, I wasn't sure what she'd heard, so I instigated a very direct conversation on the subject, and followed it up with her.
Not long after in a conversation with Mum friends, one mentioned that her DD had instigated a conversation about periods (our girls are part of the same friendship group) and I mentioned that might have come from my DD as we'd been talking about it. Another Mum, with boys, asked why I had decided to have the conversation now, it wasn't a criticism, just conversation.
I had 2 reasons for the timing. One was that I was aware that conversation and wives tails were doing the rounds at after school club, and I wanted DD to have the facts, the other was, that although I didn't expect DD to start hers imminently, I was aware that she had good friends who would (and since have) and again I wanted her to have the facts about what was going on and that we could talk. I must admit, I thought at the time I'd maybe left it late, but I think the timing as about right.
I don't always think that text messages are the easiest form of communication and doubt that anyone thinks badly of you. I also think that some parents don't really put a lot of thought about kids where else their children will get their info from if they don't provide it.