In the V5.2 GA release, the very last change made was to fix the issue of Add->table-edge producing curved lines (rather than edges). Add->Circles were doing the same thing, incidentally.
Edges in the Xtrkcad object model are very definitely straight and have a more restricted property set than lines as well (see below). So that's the first part.
The question is - are you running at current GA, (and on what platform) - or did you happen to download it very early, before I had announced it was available, (the staging ran out briefly about a three days ahead, as I recall) because I remember we had to do a rebuild to include it? Maybe we have a build that is not exactly right, for example.
This means that curved lines could be used with, or instead of, table edges as the only real difference between the two (other than the possibility of lines being curved and coloured, of course) is how the width is treated in display. A table edge retains its pixel width regardless of zoom, where a non-zero width line scales as the zoom changes. A value of -3 and color black seems to my eye to be equivalent to a table edge (although other values and other colors are possible, giving the ability to convey edges at different levels and other such things).