It is not uncommon for a Mass Cane to bloom. Often, but not always, the blooms are triggered when the plant has been under some form of stress like a temperature, light, season, or other environmental variation. These stressors will instigate reproductive instinct in the plant causing it to produce blooms.
It is recommended to remove Mass Cane blooms. The blooms are somewhat messy and draw quite a bit of energy that can negatively affect foliage quality.