Probably because of my legal training, I look at rules in a different way than others do. The first thing I do is start with the actual text of the rules. You'd be surprised how many people, including smart and educated folks, have never actually looked at the rules or the "law", but simply claim the law or rules say X. Many times this is just not the case. Even lawyers do it, although usually it's not ignorance but strategy.

For an LFMT in your state, you'd have to look up the ethics rules in the state board. It's likely they adopt the rules that the National Association for Marriage and Family Therapists, which are available here:

Code of Ethics

I don't see any rule that claims a therapist must wait two years before having nonsexual contact with a former client. Sexual relationships are explicitly prohibited and there is language in another rule about multiple relationships and avoiding exploitation, but I don't think those apply to former clients, just current ones.

The language in other ethics codes is different, and I'm bringing this up from memory, but some professions do have a time limit on "social relationships", but many have widely interpreted that to mean "sexual" relationships but the code writers were too delicate to explicitly say so. And as at least one other person has said, there is "contact" that is social or friendly and then there are social relationships or friendships. None of the language or the interpretations of the ethics rules are set in much clarity. So even the text of the rules can be interpreted differently and I guess I haven't heard much about therapists being called up to the board because they had friendships with a client after therapy.

But I think you already know because he told you that there is no specific rule but a "best practice." Again, I invite you to do your own web search to confirm this, but I believe there isn't much discussion about friendships post therapy (particularly when the therapist can no longer see a client, which is different than the issue of a client quitting because they want to skip to a friendship instead, which implicates the therapy). I think most of the ethics issues discussed revolve around sexual relationships or other potentially exploitation (e.g. going into a business together or otherwise taking the client's money). So I think it's b.s. that he is truly following the "law" or the best practice, and merely using it as an excuse to justify doing what he wants. If I were cross examining him I would want to get him to admit this is not about a "best practice" but is his decision and his choice.

The question is why, though, which is something I can't answer. Only he can. I don't think it's because he never cared about you and doesn't want you in his life in the future. I could speculate about all kinds of things, including maybe he thinks it is best for you for whatever reason or maybe he's afraid of his feelings for you or maybe he just needs a clean break from his former workplace which sounds like it was pretty awful. But whatever it is, I'm pretty sure it's about him, whether he's trying to protect you in some way or make it easier on himself. Maybe he thinks his presence in your life is negative, a.k.a. Scott Peck (I may have this wrong), if you love something let it go.

I think he's not being totally honest with you, although of course it's possible he really does believe in the "best practices." Maybe he doesn't even know what he's doing or why, but this seems like a clear bright line that is working for him right now.