I thought it was amusing. I don't think I'd call it bad sportsmanship; they just wanted a bit of fun and they made sure they were out in lane 6 to insure they didn't get in anyone's way. If someone ended up being offended by it, apologize and I think that is all that's necessary.
I'm a bit surprised at people's reactions to be honest.
So let me get this straight....we can no longer do anything "fun" with our sport because that would lead people to not take it seriously?
Why not have a tiny bit of fun when it doesn't matter?
I remember one invite that, as the last event, they had a 4x100 throwers relay. They used a twinkie as a baton. The throwers who participated from my team thought it was hilarious and were good sports about it. At one quad meet we decided to have a "steeplechase." The host coach put out hurdles set on the lowest setting and sat at where the water pit would have been and sprayed the runners with a hose. I participated in that one as part of the joke and I thought it was hilarious.
I remember that the last meet of the season that was unimportant (ie not a state qualifying meet or championship meet) all the coaches involved would do a lot of things out of the ordinary. The favorite example of this was when 2 runners from another team decided to join my team for a 4x400 relay so that we could let a runner with down syndrome anchor and have a shot at winning.
For 90% of HS runners, this will be the only time they get to compete in track and field. Yes, they need chances for serious competition, but it's okay if they have the occasional chance to have fun. Let them create those memories; it is largely harmless.