Apart from unchecking the 'Display Ancestry member tree hints in your trees' box in Site Preferences, which stops you seeing any hints from other trees, I can't see a way of filtering out the rogue hints.
So far, I haven't found spurious hints to be a problem since attaching a public direct ancestor tree to my DNA about 10 days ago. The only extra hints I have had are from my own public tree to my private tree. That said, it's still early days and my direct ancestors don't have particularly common surnames (with one or two exceptions which I will keep an eye on). However, my husband is half Welsh and has lots of people named Davies and Jones amongst his direct ancestors. The tree attached to his DNA is still private, and after hearing of your experience, is likely to stay that way.