  A neutrino outburst between September 2014 and March 2015 was discovered from
the blazar TXS 0506+056 by an investigation of $9.5$ years of IceCube data,
while the blazar was in a quiescent state during the outburst with a gamma-ray
flux only about one-fifth of the neutrino flux. In this work, we give a
possible interpretation of the abnormal feature by proposing that the neutrino
outburst originates from the interaction between a relativistic jet and a dense
gas cloud formed via the tidally disrupted envelope of a red giant being blown
apart by the impact of the jet. Gamma-ray photons and electron/positron pairs
that are produced through the hadronuclear interactions correspondingly will
induce electromagnetic cascades and then make the cloud ionized and
thermalized. The EM radiation from jet-cloud/star interaction is mainly
contributed by the relatively low-energy relativistic protons which propagate
in the diffusion regime inside the cloud due to magnetic deflections, whereas
the observed high-energy neutrinos ($\gtrsim 100\,\rm TeV$) are produced by the
relatively high-energy protons which can keep beamed owing to the weak magnetic
deflections, inducing a much higher flux of neutrinos than electromagnetic
radiation. The observed low-energy electromagnetic radiations during the
neutrino outburst period are almost as same as that in the quiescent state of
the source, so it may mainly arise as same as the general quiescent state. As a
result, due to the intrusion of a dense cloud, the neutrino outburst can be
expected, and in the meantime, the accompanying electromagnetic radiations from
hadronic processes will not cause any enhancement in the blazar's
electromagnetic flux.
