Kinda. It's just an LLM that performs function calling (i.e. the LLM "decides" when a function needs to be called for a task and passes the appropriate function name and arguments for that function based on its context). So yea an "agent" is that LLM doing all of that and then your program that actually executes the function accordingly.

That's an "agent" at its simplest -- a LLM able to derive from natural language when it is contextually appropriate to call out to external "tools" (i.e. functions).