Sound about as strange as the 368 I bought from Taiwan a few months ago, that came with a screw on filter similar to those shown above in the pic, the small lens adapter on the front unscrews and this filter then screws on in it's place. It's sold as an antiglare filter, I notice the end rotates so, I assume it performs in a similar way to a polarizing filter.
The 368 which is only available in Taiwan and Russia etc.. looks the same as the UK 358 cams available from Halfords, but with the added HDR option in the settings, which I leave disabled anyway, as I think it's only any good possibly at night. In daylight it makes the video look way to light and milky, AIS it may have some value at night.
I've not used this camera for a while, it was quite pricy too at about £135/140 with import duties added, as I prefer the small more discreet o801 cams (I have 3 of them...lol) So the 368 which no doubt is far better made and possibly more reliable, will be going on Ebay at some point. Picture quality is pretty good though, it's just the mount that's rather big and very noticeable.