Other things that have already been said on the topic in mind, here is one thing that should be added: The
greeting formula is historically an abbreviated form of actually
(something like: may your meal be blessed), which was popular when Christian religious culture was more commonly accepted and practiced. However, as everyday formulas of politeness and conduct often get abbreviated, see also
for "Guten Morgen", or
for "Guten Abend", or even
for the same thing (from "einen guten Abend!"), also the "Gesegnte Mahlzeit" lost its blessing, remaining just the prosaic "Feeding time!" exclamation.
In my personal view it is an obnoxiuos habit, but then, I have never been uncritical part of that specific German workplace culture (as I would call it rather than "work culture"), as I have mostly avoided positions in large organisations of production or administration so far where these formalisms tend to prevail.
The obnoxiousness of it lies in that it is used so pervasively even at times when no lunch is yet in sight, and when lunch is already over, and in that virtually nobody seems to have the slightest awareness that it is actually "Gesegnete Mahlzeit" - which, per se, would be a nice and decent thing to say when sitting with others at the table.