The attorney is under an ethical obligation to disclose that legal decision, which is an adverse authority, to the court.
This obligation is set forth in the American Bar Association Model Rules of Professional Conduct, §3.3.
Ostensibly, the reason is to serve the law itself by preventing a court from making a decision that is erroneous in light of the authority revealed.
In order to fall within the obligation for disclosure, the matter must meet three conditions: it must be legal authority, it must be directly adverse, and it must be from a controlling jurisdiction.
Such argument essentially seeks to present the prior authority as not being adverse at all, because it applies to sufficiently different facts.