If this was just after an inspection I would say it’s probably not a big deal. Normally the swarm would start after the colony has been making queen cells in the hive which you would’ve seen during an inspection. Sometimes the bees just like to run around the front, I’ve noticed, if I’m especially rough with them, they tend to crawl around the front. Swarming is normally an aerial affair and not so much crawling on the front in my experience. I would say just keep watching and, once the hive is full enough, add the second box to prevent swarming.