This is how you describe something that happened to someone, when the effect is still there. In the example above, the speaker's company became overwhelmed, and they are still overwhelmed.
Here's another example. If someone broke into your house and stole things from you, when you call the police you say:
I've been robbed!
The reason you use "have been" is because you were robbed, and you haven't moved anything or cleaned up yet. So your home is still in the "robbed" state. The next day, when you tell people about it, you will say:
I was robbed last night.