[jcl]

Use of "bug" to mean "defect" goes back a lot further than the computer age:

http://www.etymonline.com/index.php?term=bug&allowed_in_fram...

At the time of Grace Hopper, the term was used in engineering contexts to refer to defects in general, quite unrelated to insects. Per your link, that's why she wrote "first actual case of a bug being found" -- it was amusing and unusual to find a bug (defect) caused by a bug (insect). If this were not the case, there would be no need to use the words "first" or "actual", or even note the event.