I think Chris is right on. I assume everyone is familiar with Toby Threadgill's great essay on Assumptions?
There is another similar story about Takamura sensei that is also told. In a similar situation to the one in the article Takamura pulled a knife on a BJJer who had him in the mount. People who saw it said it appeared as if the guy levitated off him.
What it comes down to is that aikido descends from arts employed by swordsman for use in a venue that assumes bladed weapons and multiple attackers. I think you need to know this information to do aikido successfully. If you impose different assumptions either your aikido will change its essential nature to fit those new assumptions or because of the miss-match your aikido will be inefficient and ineffective in the new venue, like driving a screw with a hammer.