Not really, it was always largely figurative. The famous Mark II logbook with the moth taped to it had the note "First actual case of bug being found." - so that clearly indicates that A) the term had been in use for a while (a very long while, there is a record of Edison using it) and B) Real insects were typically not involved.
There was a article on HN a few weeks back, the link escapes me. But there was the first ever bug, an actual moth. It was taped to the error log i believe.
Edit: Brazzy explains it better and indeed seems more informed :)