https://content.mlb.com/documents/8/2/2/296982822/Major_League_Rule_21.pdf
He pretty plainly broke rule 3:
(3) Any player, umpire, or Club or League official or employee who places bets with illegal book makers,
or agents for illegal book makers, shall be subject to such penalty as the Commissioner deems
appropriate in light of the facts and circumstances of the conduct. Any player, umpire, or Club or League
official or employee who operates or works for an illegal bookmaking business shall be subject to a
minimum of a one-year suspension by the Commissioner. For purposes of this provision, an illegal
bookmaker is an individual who accepts, places or handles wagers on sporting events from members of
the public as part of a gaming operation that is unlawful in the jurisdiction in which the bets are
accepted.
Now, there is a line in there stating "in light of the facts and circumstances of the conduct" which could definitely have him in the clear even if he payed off the debt knowingly.
But I suppose if he confirms that he verified the payment then he could be opening himself up to more questions about if he was actually the one gambling or not.