As much as people hate when I say this, these messes you can expect when recruiters get involved.

Some companies like recruiters and work well with them. In these instances stories like yours don't happen because there is seamless coordination between what the company needs, what they communicate to the recruiter and what the recruiter tells the applicant.

In other instances, there is conflict between the company and the recruiter. The recruiter's goal is to get you hired in the highest paying position they can so they can maximize their commission. If that doesn't work, they will pitch you for any other similar position.

In your case, it's possible that there was miscommunication and the position was filled before your process was complete. It's also possible that the specific actuarial analyst position never existed in the first place and the recruiter tried to pitch it to the company. Recruiters are constantly seeking people because they need a bank of ready candidates to fill spots ASAP, if the need arises or somebody quits unexpectedly. Just because recruiters post positions doesn't necessarily mean that there is a specific job position out there with a specific company. Most (?) of the positions advertised by recruiters are real and specific. Some aren't, depending on how reputable the recruiter is.

TL; DR - ultimately it doesn't matter. Did you like the team? From what they (not the recruiter) told you, does the job interest you? Then don't let the kerfuffle with the recruiter bother you. That's just business.