Reminder:
This "attack" from Buu DID NOT HURT TRUNKS. The momentum from a larger physical body acting upon a stronger one still took effect due to Newton's First Law of Motion, as power levels do not negate the laws of physics in physical contests. So Trunks was MOVED by the simple act of a greater mass acting upon a smaller one. But it did NO damage to him whatsoever. And the ONLY way that is possible is if a fighter is AT LEAST twice as strong as their opponent, regardless of whether that status quo is only reflected for that single moment or is a general reflection of where one fighter stands vs another.
So, this scene PROVES that Trunks is TWICE as strong as Buu, AT LEAST, which makes him TWOFOLD OR MORE times stronger than Buu.