I'm not old enough to know but my theory is things in the programming world historically came from the computer architectural world. Computer architecture uses stacks, interrupts (events), and other things in the physical layout of the computer chip. When people were done with the hardware stuff, they created software which has similarities to hardware and thus called them the same. When people then created higher level software from lower level software, they saw similarities there as well and went from there.

Calling the language assembler might be considered potentially confusing and ambiguous, since this is also the name of the utility program that translates assembly language statements into machine code. However, this usage has been common among professionals and in the literature for decades.:

http://en.wikipedia.org/wiki/Assembler_(computing)#Assembler

I think it's called an 'assembler language' because it's the language you use to program your assembler (specifying what to emit into the binary).