Meaning of "bull" in Byron's "this is no bull, although it sounds so"

From Byron's Don Juan:

One with her flush'd cheek laid on her white arm,
And raven ringlets gather'd in dark crowd
Above her brow, lay dreaming soft and warm;
And smiling through her dream, as through a cloud
The moon breaks, half unveil'd each further charm,
As, slightly stirring in her snowy shroud,
Her beauties seized the unconscious hour of night
All bashfully to struggle into light.

This is no bull, although it sounds so; for
'T was night, but there were lamps, as hath been said.
A third's all pallid aspect offer'd more
The traits of sleeping sorrow, and betray'd
Through the heaved breast the dream of some far shore
Belovéd and deplored; while slowly stray'd
(As night-dew, on a cypress glittering, tinges
The black bough) tear-drops through her eyes' dark fringes.

I immediately thought that this meant bullshit, but then I consulted dictionaries and discovered that bullshit was coined in the 20th century. Yet it clearly means "false information" here.

If not from bullshit, what does it derive from?

Solution 1:

Bull, without the attending excrement, has meant "exaggerations; lies; nonsense" since the early seventeenth century. The excrement emerged in the early twentieth, and since then bull has seemed to be a euphemism for bullshit, while historically, bullshit is actually a dysphemism of bull.

Solution 2:

Another peculiar and interesting reference was from here

with the quote

From Middle English bull (“falsehood”), of unknown origin. Possibly related to Old French boul, boule, bole (“fraud, deceit, trickery”). Popularly associated with bullshit.

I am still searching to see if I can offer any corroborating evidence for this early version of bull.

It‘s likely this word stood alone in the early Middle English era - that is, it was not a shortened form of bullshit at the time.

Also found links to the French boler or bouller (deceive) from Word Origins by John Ayto.

There are three distinct words bull in English […] finally there is ‘ludicrous or self-contradictory statement’ usually now in the phrase Irish bull, whose origins are mysterious;

The Middle English noun was bul (falsehood) and the verb was bull (mock, cheat). However, this is still referring to the 15th - 17th century.