What you've said is just an instance of skilfull means. Ultimately, the followers of other religions (or no religion) will suffer rebirth in Samsara and continue to experience suffering. To the degree that they walk the eightfold path via their current paradigm, that will determine the quality of rebirth.

Edit: My point is that Buddhism proclaims that the Four Noble Truths are applicable to _all sentient beings_. Not that they are applicable only to Buddhists. If that was the case, then the Bodhisattva Vow could be resolved simply by the cessation of Buddhism! But the Bodhisattva Vow is a vow to save all sentient beings, not all Buddhists.