It does sound suspicious on the face of it and quite possible. Salehoo verifies that suppliers are legitimate and safe to trade to with, but we have no way of verifying where they in fact source their products from. Middlemen type of suppliers like this have become and continue to become more and more popular, but it's almost impossible to pick them, unless as in this case, you have knowledge from your supplier that rings the bells.
Now of course we don't want to mention names here because there is only anecdotal evidence suggesting that's what is going on. Of course, even if true, it's not illegal at all, in fact very legitimate. Some would even call it enterprising, where others would consider it sneaky.
It really comes down to research, are you 100% sure that your supplier is sourcing direct from a manufacturer or are they just another link in the chain, just one step us from the other supplier and there isn't an even cheaper supplier out there? .
This is the problem sometimes, once you start peeling an onion, you quite often find more layers than you expect. All comes down to research, making sure you have the best possible source.