> You don't have to take resource as something that has a negative connotation or seems insulting. The workforce within a company comprises that company's human resources. That is a widely used and accepted term, and very appropriate for official communication, which your supervisor seems to be doing.
If you believe your supervisor thinks too little of you, or the thing starts to look like bullying (which, by the look of your situation, it does not), you will have to get some more evidence on this, as him calling the company's workforce a resource is definitely not enough to hold your claim.