No, streaking on Snapchat has nothing to do with nudity. Instead, it means that two users are engaged in an ongoing "Snapstreak," which is a fancy way of saying they have consecutively opened and responded to one another's snaps. The longer the Snapstreak, the more loudly a person tends to get about the streaking. See, when you spend as much time on the app as Cool Teens™ do, this accomplishment -- denoted by a fire emoji next to each streaker's name, and a number indicating how many days the streak has lasted -- is A Big Deal.
Are teenagers getting naked and making bad decisions online? No doubt! Teens gonna teen. But they'd never call that behavior something so obvious as "streaking" -- what do you think they are, stupid or something?