Does lecturing for your PI count as a "guest lecture" for a CV? Sometimes it happens that a professor traveling has his TA or RA fill in for him/her delivering a class lecture. Is this experience appropriate for a typical engineering CV, and if so how would it be designated?

This question deals with what sounds to me a somewhat greater honor, being invited to give a lecture in another department at your school. The answers there suggest that this should be listed as a "guest lecture". A related question is whether my first scenario can be described as a "guest lecture". I have seen it described as such on CVs. But my recollection as an undergrad is when a prof mentioned a "guest lecturer" coming, it was usually a bigshot, or some specialist, not some Phd student.

I have a feeling that the professor in the first scenario would use whoever is TAing as substitute, if the TA was at all competent. I have also heard those on search committees say it looks like resume-stuffing and can do more harm than good. On the other hand, a well-received comment by @DavidRicherby in this post suggests that it is a good idea to include substitute lecturing for your PI on a CV. Do folks on search committees (whether at more teaching-oriented or research-oriented institutions) have an opinion?
I would limit the term "guest lecture" to cases where you were specifically invited to give a lecture to the course, because of your ability to contribute something special that the regular instructor could not do.  (E.g. you have special expertise on a particular topic, or experiences to relate, or notable achievements, etc.)  I wouldn't apply it to simply covering a class (teaching routine material) because the professor is away.

However, you would normally have a separate section on your CV describing your teaching experience, which would include an entry showing that you were a TA for this course.  Under this entry, you could describe your duties, which could include something like "occasional lecturing".