I’m not certain what DDG actually uses (wasn’t it Bing?), but in my experience from the last couple of months it ignores quotes substantially
more eagerly than Google does. For this particular term, a little bit of domain knowledge helps: even without quotes,
brst becchi,
brst formalism,
brst quantization or perhaps
bv brst will get you reasonable results. (I could swear Google corrected
brst quantization to
best quantization a year ago, but apparently not anymore.) Searching for stuff in the context of BRST is still somewhat unpleasant, though.
I... don’t think anything particularly surprising is happening here, except for quotes being apparently ignored? I’ve had it explained to me that a rare word is essentially indistinguishable from a popular misspelling by NLP techniques as they currently exist, except by feeding the machine a massive dictionary (and perhaps not even then). BRST is a thing that you essentially can’t even define satisfactorily without at the very least four years of university-level physics (going by the conventional broad approach—the most direct possible road can of course be shorter if not necessarily more illuminating). “Best” is a very popular word both generally and in searches, and the R key is next to E on a Latin keyboard. If you are a perfect probabilistic reasoner with only these facts for context (and especially if you ignore case), I can very well believe that your best possible course of action is to assume a typo.
How to permit overriding that decision (and indeed how to recognize you’ve actually made one worth worrying about without massive human input—e.g. Russian adjectives can have more than 20 distinct forms, can be made up on the spot by following productive word-formation processes, and you don’t want to learn all of the world’s languages!) is simply a very difficult problem for what is probably a marginal benefit in the grand scheme of things.
I just dislike hitting these margins so much.