Diversity in local practices across local immigration offices... Not uncommon, certainly frustrating at times. Live and learn. You'll get'em next time 😉
With an APEC card and no visa, you will get 30 days visa exempt just like every other US citizen entering Thailand without a visa. The APEC card is generally worthless for US because the US is a "provisional participate" (check the back of your card and you will see no countries are listed allowing visa free entry). You can use FasTrack immigration with your APEC card. That's one advantage.
Tod, you are the reason this group is valuable. And there are few others, who working along side you, that make this group #1 for visa advise. It's a shame some fool (who I have no doubt deserved to be squashed, and is probably a nut job anyway) has put you in an uncomfortable situation. My hope is you can get past this, and keep doing what you are doing. Stay strong.
If you already on the 1 yr extension of stay based on retirement, and if you are planning to later convert to another long stay type visa while in country, you are suppose to maintain all the terms of your original visa, else it creates complications. Just my experience converting from Non O to Elite.