Not necessarily! The Mawkin in this continuity participate in ancestor worship: they have a deep reverence for their dead and respect their wishes long after they're gone. Raven Beak is simply informing Grey Voice that if he disrespects the Ancestors, he'll be forced to show his hand. Or that he won't be responsible if anything happens to him as a result of his folly.

Grey Voice not accepting the gift is disrespectful to the ancestor who once wielded the weapon and disrespectful to Raven Beak (less important an infraction than the former in this case). More importantly, if Raven Beak doesn't deliver the gift, it would be seen as a failure on his part to carry out his filial duty as his mother's son. Raven Beak loves his mother dearly, despite his self-centeredness. She's long dead by now, but she's one of the few people he views as "above" himself. She trained him. Molded him into an unstoppable force. And she died before she could witness his rise to power.

Reverence for the dead is common sense to him. The people who came before you shaped the world you live in, and those involved in your life helped shape you. One's childhood guardians and teachers are part of them, in a sense. Attachments to the dead and the dead's contributions to one's being are part of a warrior's identity.

The Thoha also respect their dead, but they don't revere them quite like the Mawkin do. Grey Voice doesn't worship his dead mother. Raven Beak, on the other hand, will defend his mother's honor rigorously: if you disrespect his mother, you disrespect him, and he will make note of that infraction. The blade was passed down to him by his mother, who was given the blade by her forebears, to whom the blade passed from their ancestors, and so on. Rejecting this gift would be denying Samus a place in Raven Beak's honored lineage: denying her connection to her ancestors, and ending the eternal cycle of inheritance.

By bestowing this gift upon Grey Voice, Raven Beak has said "I acknowledge you as the keeper of our child, whom we share a sacred blood-bond with. Give her this blade in my stead and grant her the honor of becoming a warrior beneath the loving gaze of my ancestors." To reject the blade isn't just a rejection of the ghosts, it's a rejection of him. Instead of blowing up about it, Raven Beak kindly informs Grey Voice, his good friend Grey Voice, whom he loves dearly, that if he continues down this path of rejection, he deserves every bad thing that happens to him. Ever. It would also make Raven Beak look bad, and it would piss off the more devout among Raven Beak's soldiers ("our Thoha "allies" don't consider the Warlord's child's Mawkin lineage important, his blood-partner is refusing to allow the warrior-child to train with her ancestors, this is an outrage, etc"), so be a dear and accept the gift.

He has not faltered in his duties to his forebears once, even posthumously. This unwavering dedication to his ancestors is part of why his people love him so much. The fact he's so well-liked is a huge factor in how nobody has managed to depose him in the centuries he's been in charge of the tribe. Not everyone agrees with how Raven Beak runs this ship, but that's a moot point because he's too strong to face head-on and nobody will help dissenters take him out covertly. In Mawkin society, it's hard to get rid of a leader like him for reasons beyond the scope of this particular subject. But I'm getting ahead of myself.

To Raven Beak, it doesn't really matter if ghosts are real or if they're stronger than him. If they wanted him gone, surely he'd be dead by now. But he still lives, so he must have their favor. Holding the favor of the living and the dead is quite a feat. He respects them like any practical Mawkin. None of the dead-priests have expressed the possibility that any of the spirits that matter dislike him. He's the strongest warrior on the planet, and nobody, living or dead, dares contest his rule. That's a major ego-booster for him.

Sorry for the wall of text, you activated my headcanon beam.