X turned out to be true

Basically, without knowing the veracity (or evidence) supporting either claim, pro or against, we only have a set of opinions.

By bringing X into the dispute without knowing its relevance to the argument we're dealing with an Ad hoc rescue:

Claim X is true because of evidence Y.

Evidence Y is demonstrated not to be acceptable evidence.

Therefore, it must be guess Z then, even though there is no evidence for guess Z.

From Dr. Bo:

Ad Hoc Rescue
ad hoc

(also known as: making stuff up, MSU fallacy)

Description: Very often we desperately want to be right and hold on to certain beliefs, despite any evidence presented to the contrary.  As a result, we begin to make up excuses as to why our belief could still be true, and is still true, despite the fact that we have no real evidence for what we are making up.

Logical Form:

Claim X is true because of evidence Y.

Evidence Y is demonstrated not to be acceptable evidence.

Therefore, it must be guess Z then, even though there is no evidence for guess Z.

I'd say this is a version of the galileo fallacy - in that one, "Everyone thought Galileo was wrong too, but he turned out to be right" is used as justification for believing someone spouting any old nonsense.

The rebuttal to this is that while there may be a few examples of things which seemed ludicrous turning out to be true, the vast majority of ludicrous seeming things were not true.

The two statements are merely opinions, while the third "supportive" statement might be merely an analogy, and only weak and just contentious.  At a minimum, the proponent needs to clarify the validity of the analogy.

If the only basis for supporting A is that the two (A and X) were similarly initially refuted, it is an example of non sequitur and argument from ignorance