Well, keep in mind that couple key players were missing. Especially Anamul Haque, Abul Hasan Raju..
People said the same thing when UAE beat Bangladesh and that UAE has a bright future etc. etc. But the fact of the matter is, if you dont have a consistent pipeline, sponsors, crowd, infrastructure, any game will eventually die off... For instance, take Kenya as an example, reaching the Semis in world cup and then what happend? Unless Afghanistan can get fundings, crowd, cricket brains behind their team, they will have a spike but when the core set of players retires or are out of form, they wont go far.
Bangladesh losing to Afghanistan is a signal to BCB that they can't keep ignoring the youth team and be completely absorbed into the political, financial, international side of cricket,, they have to invest in good U17, U19 programmes, game development and get quality coaches. We let go of Fernando, Carlton, Shawn, De Winter etc. many years ago and never filled those roles and now we are seeting the downslides...