As you will have seen upthread, it's long been the case that BCN does not have a lounge for Gold Star Alliance passengers in economy, nor Fast Track (Fast Lane). And that's also clearly laid out in TAP's website
https://www.flytap.com/en-gb/at-the-airport/lounges
https://www.flytap.com/en-gb/at-the-airport/fast-track
The agent was wrong, I don't see the point in them lying, what's the benefit of that? But given the agent probably works for 8 different airlines each week it wouldn't be surprising if the agent got it wrong, given than other airlines take a different approach to TAP.