i hear that if u summon a storm thrall it summons a alronach instead

What?
The elemental thrall spells are all permanent Atronachs with different stats but they are all atronachs.

thralls are more powerful than atronachs

You need to be clear when you ask a question as you essentially asked if Storm Thrall was bugged for summoning an atronach. To answer your actually question no its not bugged