"Acoustic bike" is gratingly cringeworthy, for sure. Adolescent male humor, equivalent to the snickering heard when the "iPad" was released (though without the nervousness about a female bodily function).

Not to worry, though. The names used out in the world (outside of forums, that is) for the two types will continue to be "bike" and "ebike," just as the English-speaking world has had no problem with the occasionally ambiguous "bike" versus "motorcycle" (or "motorbike," the term my Solihull, Birmingham-born girlfriend uses to refer to any ICE bike).