It depends on how they "won". If it was a full hearing with a jury and everything, that's public record. If it's arbitration, that's probably not public record.

Bragging about a "win" in arbitration, and making something that's not a public record, into a public record, is usually a problem.

With the current wording, while you can infer from context, the outcome of the case, it isn't explicitly stated by the lawyer. The largest disclosure here is from the party that feels they were "wronged", and the lawyer is simply stating that "this person wasn't my client" (more or less). You fill in the rest.

The fact that the commenter was not their client is not disclosing any private information, nor any information about the matter that's being discussed. It's a simple statement of irrefutable fact. (Or fact that can be proven at least)

If the lawyer crosses a line by discussing case specifics, like what the matter regarded (divorce, custody, property, whatever), or the outcome of that case, when it is not a matter of public record, can land them in serious hot water.

I would assume, again, from context, that the matter is not presently a part of public record.

Maybe the lawyer lost the case. The response is even more brilliant in this case !!