I'm not sure how much telemetry Teslas actually send (do buyers really tolerate their absurdly expensive car reporting their every move back?), but in any case I would assume it all gets stored for bulk processing. Twitter's pretty different; when [insert celeb with 100m followers here] tweets, that tweet should show up for anyone who's looking at their profile, immediately. And the like and retweet counts should update for everyone looking at the tweet that just went out to 100m people (actually, it would be possible for Twitter to fudge this bit, but they don't seem to).

These might seem on the face of it similar problems, but really they're not at all. Ingesting lots of data is ~trivial; dealing with lots of data in realtime somewhat less so.