But let's see if the inverse is true as well. If you deeply deeply deeply cared about your job (eg: it's your startup and you have exactly 12 months of runway, but it takes 4 months to source, vet, hire and onboard someone), would it matter to you that someone cheated you out of a third of your runway?
The truth is likely somewhere in the middle. That should answer why someone who is likely to reasonable care about their job and would likely experience a serious setback in their work would be really upset about the OP's actions.