No. This is an illogical inference. Unless Beth explicitly says only ONE companion (human or non human) can occupy a custom made settlement at any given time. All 12 of those companions might be able to inhabit exactly one settlement (similar to custom mod player homes in Fallout 3 and NV). Or we might get the option to settle any number of them in 1E+06 possible homestead building site locations across the wasteland....
The point is nobody knows what the settlement number limit is except Beth. Anything posted until then is 100% concentrated fan speculation.
edit: based on your reasoning, it would make more sense to assume at least 12 settlements at minimum...