Data that i can visual see as being passed over is the
- Mii associated with Streetpass including
- The Mii
- Mii's Name
- Welcome Message
- Last Game Played
- StreetPass Quest puzzle
- your Sate/Province
i didn't have Streetpass Plaza opened instead i was just sitting on the home screen highlighted the GameCard game i had in at the time.
I can confirm this from like the only Streetpass hit i got when i had my 3DS on while i was driving around during my driving lesson. this is the information i got
- The Person's/Mii's name (don't remember)
- Their Mii wearing a pikman hat
- The Welcome Message: "hello my friend"
- The Mii said they had been playing Super Mario Brothers recently
- In Streetpass Quest they had a bunch of puzzles i didn't have
- Streetpass Plaza brought up a map and highlighted Victoria
the information above was received by my 3DS before connecting to the net as when i get home before turning the net on i check how many coins i have gained and noticed i had a notification. calculating when i had gotten the Streetpass hit i could guess that i got hit while i was driving on the highway roughly 10 minutes away from home when i passed someone's house.
connecting to the internet as i passed by would be impossible as i doubt someone in this day in age is stupid enough to have an unencrypted wireless network (the router i have had all ready been secured by my ISP) and even then i'm pretty sure the 3DS doesn't connect automatically to wireless networks (though this may only apply to encrypted networks as i had to scan for my home one despite being next to the router)
As for the delay, that could be processing, in Bryan C. answer in the link they posted it seems the header information will contain a list of StreetPass services enabled on the device, so then the hit you got had a number of services enabled and your console make take some time to sort and prep the data to the applications for when you start them up, extra time may be taken if it's doing a check to only prep data for application you have yourself, ofcause the only games i have which had Streetpass is Etrian Odyssey Untold and Bravery Default and neither one got a hit when i started them up so that's my only evidence