An enquiry is an informal question about whether a player is available and roughly what it would take. A bid is a formal written offer with a fee and terms attached, which the selling club must consider and answer. Most reported transfer interest never gets past the enquiry stage.
The gap between the two is where most transfer reporting lives. A club asking a question costs nothing and commits nobody, and it can be briefed out as interest, so a great deal of what reads as an approaching deal is one phone call that went nowhere.
A bid changes the position because it forces a decision. The selling club has to respond, the player usually learns of it, and a rejected bid establishes a number the buying club will have to beat. That is why clubs sometimes hold off bidding formally until they think the answer will be yes.
The ARCHV treats the distinction as an editorial line rather than a technicality. An enquiry is not a bid, a bid is not an agreement, an agreement between clubs is not a completed transfer, and a story that blurs those steps is describing a deal that may never happen.