My first thought is that one should not fall for the post-hoc ergo
propter hoc fallacy. That one passage only preceded the other is no
proof the two are related.

To evaluate fully this question, one must be fortunate enough to drift
over the clear water of Lake Tahoe and gaze downward into its depths
as Twain did and later recalled. Looking down from a high vantage
point is the only way one can describe this experience. Today,
awestruck tourists commonly compare this inspiring sensation to flying
on an airplane. In the 19th century, airplanes did not exist, but
hot-air balloons did. Lake Tahoe is one of only very few large lakes
throughout the world where one can experience this feeling.

One might be tempted to conclude that if a passage was plagiarized, it
must not be true. However, plagiarism does not mean the subject is
untrue, only the culprit author’s personal values are questionable.

At worst, Twain might have borrowed the literary treatment, but the
accuracy of his observations is indisputable. His description of the
offshore distance, size, and geologic classification of the boulders
is specific to the North Shore of Lake Tahoe. These conditions only
occur within the zone offshore of his campsite on Stateline Point.

David C. Antonucci
Author of Fairest Picture - Mark Twain at Lake Tahoe