The cell being built at the bottom of the frame like that suggests that they planned it, either to replace an old queen that's wearing out, or to make a new one to swarm (emergency queen cells to replace a dead queen will be on the comb anywhere they can find brood of the right age to groom into a queen). If the colony was running out of room, then they are likely to have been planning to split the hive. Both of those together (crowded hive and pre-planned queen cell) tend to suggest swarming activity, especially in spring.