Sounds like a few of the finer details were mixed up.

https://www.scientificamerican.com/article/just-how-harmful-...

> A maintenance worker had used an abrasive floor cleaner, instead of the usual mild detergent, to wash out cages and water bottles. The acidic solution scarred the hard, polycarbonate surface of the plastic and enabled a single chemical culprit to leach out—bisphenol A (BPA).

What's special about the surface that doesn't let BPA to leech out? Is it a different composite used on the inner surface or does it have to do with something like how water is strong until the surface tension is broken?

At a minimum, roughing up the surface of a material will substantially increase its surface area.

> But during the manufacturing process, not all BPA gets locked into chemical bonds

Quote from the article. The plastics are polymers - monomers linked into chains, but the linking is random and this would be a plausible explanation.