Now let's see what was the thread topic? Oh ya, inverts adding to the bioload
I would actually suggest the inverts themselves where not the cause but rather something else. If water was introduced from the LFS
bag, that could have added something or possibley the test kit was not reading correctly unless it's still reading as such.
There is also the possiblility of ammonia appearing after the tank is suspected of cycling. It part of the tanks maturing process and small elevations in these numbers can and will happen. They are usually very short lived and often not noticed by hobbiest. You can never know what the rock contains and the possibility of a hitchiker up and dieing is more than possible at any stage which would contribute to the ammonia.
Personally I would call this coincidence but a few water changes should solve your problem for the time being.