Um...what came before "One of those quaint astrological holus-boluses, quite all right.", do we know? That is, was it anything that might have added to the context?
Based on these two lines, I would guess* that something quick and fairly catastrophic had occurred; a sun spot erupting, or a "shooting star", or even a nova.
*Assuming that the author knew the meaning of holus-bolus and was not, as you suggested, simply putting it in for the "sound effect" as it were.