I will say that the message could be a bit more clear in cases like this. Your strength is currently too low to hold it with only one hand. Unless a weapon is tagged with a specific flag (ALWAYS_TWOHAND), the game will determine whether or not it takes two hands to use based on the item’s weight/volume versus your current strength. Since combat knives do not have that flag, they can be either one or two handed weapons, depending on your current strength stat.