Ideally, you would send your BTC to the mixer and it would forward you on the same amount - fee from a completely separate transaction chain of Bitcoins so that it cant be traced, but in reality, can it work like that unless the mixer has a lot of BTC. If the Mixer has little BTC or is new they might not have funds on another chain to send to you and then they just forward your BTC back to you which has the same trail.
Could someone explain if that is likely the case in this scenario? or are there other technologies at work here?
They wouldn't.
The whole point of mixers is to eliminate the link between your coins and the coins sent from the service. Most mixers does this extremely well, by sending you funds that are completely unlinked to you. In most cases, the mixer takes your Bitcoins, send it to several addresses to obfuscate the link, consolidate some of them and keeps it for another user. Any competent mixer should not send the funds back to the user in the same session. Different mixers of course will have different methodologies and methods to avoid detection.
As with the link mentioned above, the privacy was broken through blockchain analysis and it would be a good read if you want to know the rationale behind it. CoinJoin does not break the link, by the way. It merely obfuscates them but the link is still there.