I'm agree that the real estate agent involved is doing a poor, quickie kinda job here. I've come across such before (thus, the bl*ody headache that followed one case!).
Not only should he verify important details about you, the (prospective) tenant, e.g. where you work, employment letter, HKID, and if necessary: visa-type, for the landlord, but also, YOU should be satisfied about what's in the contract, AND that the person, "the landlord", who will sign the Tenancy Agreement IS indeed the one who owns the property (or has the power of attorney "right" to complete said transaction IF there's more than one owner), etc, etc.
All this should be checked - outlined clearly; the agency should obtain copies (from researched originals) before the final meeting/decision to sign the lease.
Then the contract should be registered with the Rating & Valuation Dept (RVD) asap - usually part of the agent's job, where details of the landlord's address and contacts are required in the form... And a copy of the simple stamp-duty registration/receipt could be given to the tenant to attach to his duplicate TA, if so requested.
So... your agent should have details of the landlord filed somewhere; OR is hoping you'll eventually "back off", perhaps... since he's been told NOT to hand it over!? Just PERSIST