  The evolved stages of massive stars are poorly understood, but invaluable
constraints can be derived from spatially resolved observations of nearby red
supergiants, such as Betelgeuse. Atacama Large Millimeter/submillimeter Array
(ALMA) observations of Betelgeuse showing a dipolar velocity field have been
interpreted as evidence for a projected rotation rate of about $5\,
\mathrm{km\, s^{-1}}$. This is 2 orders of magnitude larger than predicted by
single-star evolution, which led to suggestions that Betelgeuse is a binary
merger. We propose instead that large-scale convective motions can mimic
rotation, especially if they are only partially resolved. We support this claim
with 3D CO5BOLD simulations of nonrotating red supergiants that we
postprocessed to predict ALMA images and SiO spectra. We show that our
synthetic radial velocity maps have a 90% chance of being falsely interpreted
as evidence for a projected rotation rate of $\mathrm{2\, km\, s^{-1}}$ or
larger for our fiducial simulation. We conclude that we need at least another
ALMA observation to firmly establish whether Betelgeuse is indeed rapidly
rotating. Such observations would also provide insight into the role of angular
momentum and binary interaction in the late evolutionary stages. The data will
further probe the structure and complex physical processes in the atmospheres
of red supergiants, which are immediate progenitors of supernovae and are
believed to be essential in the formation of gravitational-wave sources.
