Their approach is still agentic in the sense that the LLM must make a tool cool to load the particular doc in. The most efficient approach would be to know ahead of time which parts of the doc will be needed, and then give the LLM a compressed version of those docs specifically. That doesn't require an agentic tool call.
Of course, it's a tradeoff.
LLM's have always been at any time limited in the amount of tokens it can process at one time. This is increasing, but one problem is chat threads continually increase in size as you send messages back and forth because within any session or thread you are sending the full conversation to the LLM every message (aside from particular optimizations that compact or prune this). This also increases costs which are charged per token. Efficiency of cost and performance/precision/accuracy dictates using the context window judiciously.