  We identify a low-metallicity ($12+\log({\rm O}/{\rm H})=7.59$)
Ly$\alpha$-emitting galaxy at $z=5.943$ with evidence of a strong Balmer jump,
arising from nebular continuum. While Balmer jumps are sometimes observed in
low-redshift star-forming galaxies, this galaxy also exhibits a steep turnover
in the UV continuum. Such turnovers are typically attributed to absorption by a
damped Ly$\alpha$ system (DLA); however, the shape of the turnover and the high
observed Ly$\alpha$ escape fraction ($f_{\rm esc,Ly\alpha}~\sim27\%$) is also
consistent with strong nebular two-photon continuum emission. Modelling the UV
turnover with a DLA requires extreme column densities ($N_{\rm HI}>10^{23}$
cm$^{-2}$), and simultaneously explaining the high $f_{\rm esc,Ly\alpha}$
requires a fine-tuned geometry. In contrast, modelling the spectrum as
primarily nebular provides a good fit to both the continuum and emission lines,
motivating scenarios in which (a) we are observing only nebular emission or (b)
the ionizing source is powering extreme nebular emission that outshines the
stellar emission. The nebular-only scenario could arise if the ionising source
has `turned off' more recently than the recombination timescale ($\sim$1,000
yr), hence we may be catching the object at a very specific time.
Alternatively, hot stars with $T_{\rm eff}\gtrsim10^5$ K (e.g. Wolf-Rayet or
low-metallicity massive stars) produce enough ionizing photons such that the
two-photon emission becomes visible. While several stellar SEDs from the
literature fit the observed spectrum well, the hot-star scenario requires that
the number of $\gtrsim50~{\rm M}_\odot$ stars relative to $\sim5-50~{\rm
M}_\odot$ stars is significantly higher than predicted by typical stellar
initial mass functions (IMFs). The identification of more galaxies with similar
spectra may provide evidence for a top-heavy IMF at high redshift.
