There are intricacies to how Silver Slugger Award winners are chosen. It's managers and coaches who do the voting, and they are instructed to vote according to their own impressions and players' statistics. You can imagine there being agonizing choices, and the Seattle Mariners were arguably on the wrong end of a couple this year.
But then you have Cal Raleigh winning the Silver Slugger for American League catchers.
It might not be the highest honor he claims this year, as he's officially up against Aaron Judge and José Ramírez for the AL MVP.