can this be called stock buy offer at all?
Not really. However, that misnomer does not strike the legality of that agreement.
Under contract law, labels in isolation really have no meaning or relevance. They become relevant or meaningful only with respect to the rest of the language of the contract. In the agreement you mention, the common meaning of ownership is superseded by the conditions and the intent that can be ascertained from the contract altogether.
There are better terms (such as holdings or loan) to preempt confusion about the fact that the company retains the ability to recover the stock. That ability is evident from the company's contractual right to force the buyback in the event that your friend no longer works there.
Regardless, during the time the stock is in your friend's possession, he benefits from that possession just like any actual owner of a stock of same characteristics. For instance, in the case of dividend paying stock, your friend earns the dividends without an obligation of reimbursement once he no longer works at that company (or at least you did not specify otherwise). Similarly, your friend's stock might grant voting rights, which are inherently irreversible once these are exercised.
Something your friend should ascertain from the contract and the characteristics of the stock is whether the stockholder is allowed to transact it (think of selling it or short-selling it). Although unlikely, there might also be financial derivatives of which the underlying asset is that stock. Short of actual ownership of stock, your friend might still be able to perform trades as an owner would, and then buy the same quantity of shares in the event that he needs to return them to the company.