There are several elements in "Texan Steer" that do give me pause and think
that the sketch has a Twain whiff about it.

1) Twain did write a number of reports when he was living in and
contributing to California newspapers about animals (dogs) running in the
street and a being a menace to the public.

2) The final reference to improving the undertaking business if the steer
was not captured -- Twain had a particular aversion to that business
enterprise. (See "Mark Twain's Quarrel with Undertakers" online at
twainquotes.com).

3) One curious angle that I found when I looked at _Mark Twain's Lexicon_
for the word "corned" in quotation marks -- The documented usage according
to the _Lexicon_ was in the 1910 edition of _Mark Twain's Speeches_ in a
speech titled "The Union Right or Wrong? Reminiscences of Nevada." That
1910 version of the speech contains a passage: "We found him standing on a
table in a saloon with an old tin lantern in one had and the school report
in the other,  haranguing a gang of "corned" miners ..." (_Speeches_, 1910,
p. 272 -- available in the Oxford Edition, 1996).  Searching for that
identical phrase turns up an edited version that was used in _Roughing It_,
Chapter 43.   However, the passage had been edited to read: "haranguing a
gang of intoxicated Cornish miners..." (_Roughing It_ University of
California Works edition, 1993, p. 280). There is no textual commentary
regarding this change or how it appeared in the original manuscript, if it
exists.

I think a good argument can be made that Twain did use the phrase "corned"
at least once in his notes and that it was later edited and/or refined in
such a way to implicate Cornish miners -- who may not have even been
Cornish.

Barb