Londoners reported being able to read newspapers at midnight for a couple days.
Are you sure that's from Tunguska, and not the solar storm of 1859?
I'm kind of leaning towards a volcanic eruption, particularly when an alleged scientist proclaims "would have been out
of all proportion to ones we see in recent times".
This is now, that was then. Maybe Tambora erupted spectacularly a number of times in human history, before
the early 19th Century blast.