I remember pictochat getting banned on my school bus because we were saying bad stuff like “butt” and “ass” and probably drawing pictures of dicks. Ahhh what a time to be alive
DS had full WiFi, just nothing to do with it unless a game needed it, but yeah pictochat did use that receiver. As far as I know it was a proprietary protocol so not actually WiFi, but same antenna and bandwidth and everything.
I feel like I read it uses ad-hoc capabilities not unlike what's used on Switch nowadays. Ad-hoc networking isn't used that much though outside of that for some reason.
It used wifi. Can't remember if it also had IR communication, like the GBC. It's been ages since I had a DS, but I'm pretty sure that there was another handheld other than the GameBoy Color that had the IR stuff. Nobody used it though, because it fuckin sucked.
The DS did have an IR sensor but (I'm pretty sure, don't quote me too hard here) a majority of the local communication was using either wifi or a proprietary wireless connection using the wifi antenna/chip.
I specifically remember Pokemon Black/White having an IR quick-trade option where you had to put 2 DS's back-to-back and being really confused about it because it seemed useless since it took so long to actually work.