Flash mobs are commonly portrayed in the media as light-hearted events intended to surprise bystanders. Meanwhile, academic literature features a number of explicitly political interpretations of flash mobs. However, to date, no empirical study has addressed why individuals organize and take part in the internationally spread mass events organized by the most popular contemporary flash mob incarnation, the Urban Playground Movement (UPM). In this paper, we place Budapest's UPM on an entertainment practice versus social movement mobilization spectrum. Our interviews with the leaders of the largest Hungarian UPM organization show that the functioning of the UPM in Budapest heavily relies on social movement continuity, where organizers see their events as ways to reclaim public spaces and to prefigure more social cities. However, among participants surveyed at the most notable yearly UPM event, the International Pillow Fight Day, we found fun as the primary motivation for participation, thus showing movement discontinuity. We conclude that the UPM in Budapest is a collective action, but not a social movement. Secondly, we find that the UPM exhibits 'thin' diffusion both in its reliance on individual activists over coalitions and in its usage of commercial social media as its diffusion infrastructure. Lastly, our results show that UPM collectives can act as 'containers' of social movement frames, implying that these playful groups could function as vehicles in the spread of protest in movement milieus. Our key finding that UPM is not a social movement contradicts the numerous academic interpretations of flash mobs as outright political events.