And if said boss isn't trying anything, he still ought to understand the signals it sends sufficiently well to either 1) not do it, 2) invite more people (and make that clear in the e-mail), or 3) make it something much more casual than drinks on a Saturday night.
If he doesn't understand that, he'll be the kind of manager that creates liabilities by leaving e-mail trails of questionable invitations that might get caught up in discovery if/when something happens.
If he doesn't understand that, he'll be the kind of manager that creates liabilities by leaving e-mail trails of questionable invitations that might get caught up in discovery if/when something happens.