First, a thought about the question: you ask whether you've "acted immorally according to virtue ethics." You might be trying to understand what light virtue ethics in particular casts on a case like this, or you might be interested in whether what you did was wrong, period. In either case, I don't think we have enough information to say. But let's take the cases in turn.
Some views provide what's supposed to be a criterion that we might be able to use rather like an algorithm to figure out what's right or wrong. Utilitarianism would tell us to do a sort of cost/benefit analysis, toting up the goods and the harms and deciding whether one action is better than another by seeing how the arithmetic works out. Kantianism would direct us to apply the Categorical Imperative in one or another of its forms. (For example: we might ask whether what we're considering would call for treating someone merely as a means to an end.) Virtue ethics doesn't work that way. It's often understood as telling us to do what a virtuous person, aware of the situation and properly informed, would do. We can get a grip on that by asking what virtues are relevant—honesty, for instance, or fairness or courage or kindness. But the list of virtues is open-ended, and even once we've identified some relevant ones, there's no recipe for saying how they apply in a particular case. For example: a person with the virtue of honesty isn't necessarily someone who unfailingly tells the truth. Rather, a person with this virtue knows when truth-telling is the right thing, and acts accordingly. My own view is that it's a virtue of virtue-ethics that it has this open-ended character, but not everyone feels that way. In any case, it's hard to say with so little information just how the virtuous person might act in your situation without knowing what's at stake and what the law actually is forbidding.
The fact that you ask your question in the first place suggests that, virtue ethics aside, you may not be sure you did the right thing. If you told your former client what the law actually calls for and he chose to break the law anyway, then it's not likely that you breached any duties of professional ethics. However, that doesn't necessarily answer the larger question; things can be in accord with professional codes of ethics and still be wrong. If you were implicitly encouraging him to commit some sort of fraud, that would be at least somewhat worrisome even if this particular sort of "fraud" is something most people wouldn't see as wrong. The worry is that we have at least some duty to obey the law even when the law is less than ideal. One reason: picking and choosing among laws might weaken your own overall respect for the law, and might likewise make other people respect the law less. Again, this isn't conclusive and a lot would depend on the details. But as a lawyer, you arguably are held to a higher standard than most people when it comes to matters of the law. It doesn't sound like you literally broke your professional oath, but we can still ask whether you behaved as we would ideally like lawyers to behave. Did you caution your former client? Did the way you answered his question suggest that you take the general maxim that we should respect the law seriously? Or was there a wink and a nod? How good are your reasons for thinking this kind of "fraud" isn't really wrong?
I don't know the answers to any of those questions. But if you're trying to decide whether you acted wrongly, they're the sorts of questions I'd say you should ask.