It really isn't a "filter" any more. It's a sorting algorithm. It works the same as a Google search. 100% matches sort to the top, if there are any. Then you get 99% matches, 98% matches etc etc with the word "missing" if one of the parameters is not in the results returned.
The objective is that if you can't find a 100% match, you'll give up one or more of your required amenities, and pick something else.
Obviously, that was planned to result in more bookings, although I'm not really convinced of that, since the person searching was planning on booking already. I'm also not sure it contributes to customer satisfaction. Probably a slightly unhappy customer before the booking even starts, since an amenity a person was looking for is going to be missing.