By design, the pack filter works the opposite way any normal person would think it should. It's inclusive rather than exclusive. So, when you select certain packs with the filter, the results will show you builds that use those packs AND any other packs. There's no way to exclude packs from the search.
The reason the filter works that way is to give you FOMO. If you were able to search for builds that just use packs you own, you'd be less likely to feel like you need to buy more packs.
I agree with the suggestion that if you see a build you like and it uses packs you don't own, actually click the unowned-pack icons to check which items are used from those packs. If it's not very many, I will often download those builds anyway. The game will make substitutions for items you don't own when you place the build on a lot. Also, the gallery is still riddled with bugs, one of which is that sometimes a build will be flagged in the search results as though you don't own all the packs, but when you click to see the details, you might see that you actually do have all the packs and the build was flagged for no reason.
