Logical Operators Precedence in Search Bar: OR before AND ?

(For those who don't know the "advanced" search techniques, here's a summary: https://www.reddit.com/r/TheSilphRoad/comments/6znldb/new_update_version_0750/).

I've done some experiments and found this.
If you input "Grass & Poison, Psychic", it will be interpreted as ((Grass AND Poison) OR (Grass AND Psychic)). Therefore, the results will include (Grass AND Poison) type Pokemon like Venasaur and (Grass AND Psychic) type Pokemon like Eggy. Not (Grass AND Poison) types and all Psychic types.
Why? Isn't the convention of logical operator precedence AND before OR?