The question on the British citizenship registration form asking whether a parent 'has always had the same nationality' concerns only that individual parent's personal nationality history—not a comparison between parent and child [1]. If the parent was born Chinese and has never acquired, held, or renounced any other nationality throughout their life, the answer is yes. You should list Chinese as the parent's nationality in the relevant fields.

The son's BNO status is entirely separate and does not affect how you answer about the parent's own background [2][3][4]. The Home Office expects such discrepancies between parent and child nationalities in BNO-related applications and uses the parent's section to verify their continuous immigration and nationality record independently [1]. Focus exclusively on the parent's own nationality changes—or lack thereof—when completing that section.