It could have been halo gel polish with a hard gel underneat, or halo gel polish encapsulated in hard gel etc. I don't think anything you did here was at fault. Clients most likely don't pay attentin or don't know what is on their nails. As an example, I don't pay attention what my hairdresser use on my hair.
What I normally do in these situations, is try to soak off for the normal amount of time in case it is just gel polish, if not much has happened I will file down the product as I would with a hard gel. If I can see that the nail is fine underneath, and I don't require soaking off the small thin layer of product, I will simply leave that to grow out and proceed with my application.