When someone leaves or is laid off, it's not uncommon for their job to be absorbed into everyone else's. This is far from fair, but that doesn't stop it from happening. There is a right way and a wrong way to do this, though. If you're going to give everyone else more work, you should make sure it makes sense with the workload they already have, and if that means taking some tasks off the table, then you should take some tasks off the table. Or you should be given a raise commensurate with the amount of extra work you're doing. This doesn't always happen, though, and sometimes employees are just expected to take on more than they're comfortable with just to keep their jobs. This was an extreme example of this, and one that would have gotten under anyone's skin, even the chillest employee.
Nobody wants to have to carve out time from their workweek to do someone else's work. You probably have enough to do of your own accord; you don't need someone else's workload to round it out. Especially if it's something you're not necessarily trained to do. A receptionist is a big job in and of itself. You need someone at the front to field all sorts of things that come through the door. You have to be attentive and available, and it's not a great time to do other work. So why would you split that up between people who probably don't want to do it?