Now it gets interesting, it was an IED per FBI:
http://www.twincities.com/2017/08/05/no-injuries-after-explosion-at-bloomington-islamic-center/
Someone threw it but this is an interesting development. Who’d go through the trouble to make an IED? Could be Muslim, could be others. First instinct is the former.
From photos and tv available online the damage appears to be minimal. The lower half of one of the twin glass entry doors is broken. Apart from partially burnt vertical blinds/curtains at the broken glass there wasn’t any fire or smoke damage visible around the opening or elsewhere on the exterior. “IED” seems like embroidered language.