This historian disagrees. Any such spontaneous remark made in a particular situation must be viewed, from a Certeauvian point of view, as a highly contingent bricolage which arose in a specific cultural context which presented a limited toolkit. From a Bordieuvian perspective, it must be regarded as conditioned by the habitus in which it occurred and considered with reference to the specific cultural, geographical, and architectural features of that habitus Viewed through a neo-Foucauldian lens, one might suggest that you are engaged in a violent act of hegemonic (mis)appropriation and re-valuation of a conditional statement which ignores or denies the statement's originally contingent and fluid nature, then reifies it for the express purpose of delineating and enforcing a disciplinary boundary.
Any academic historian worth his or her salt operating in the 21st Century would be well aware of the work of de Certeau, Bordieu, and Foucault, and even if proceeding along alternative lines of analysis, would provide a substantive argument as to why the sort of "contingency analysis" found in their work is not appropriate to the matter at hand, even if only implicitly. This element is entirely lacking in your presentation and all that is left is a corollary assertion to a reductio ad absurdum that because no such gun is visible that the the remark is (as you said explicitly) unambiguous and (as you suggest implicitly) supports your position. As historical reasoning, this is sophomoric at best, meretricious at the mid-point, and intellectually dishonest at worst.
The onus is not on another individual to prove the negative of your assertion -- this is a classic near-impossibility. Even were one to concede that there is no clear disagreement between the selected quote and your broad assertion, that does not make the quote a confirmation of your assertion. If you assert that a spontaneous statement made by a specific individual to correct a single aspect of a single individual's technical capacity on a particular occasion at a particular site may be taken to have a broader and more universal meaning, the onus is on you to effectively bound and nullify any and all contingencies that might undercut your claim. You have done no such thing, choosing rather to make emphatic but poorly grounded assertions based on cherry-picked evidence. This would suggest that while you know the phrase "methodological rigor," the efforts of your instructors to introduce any significant measure of such rigor to your working process, or to give you any working knowledge of what methodological rigor might entail, seem to have been less successful than one might hope.
You may wish to consider the extent to which your position is rather different from that of a non-academic individual who takes an amateur and avocational interest in a historical subject, to the extent that such an individual is wholly responsible for his or her own views and argumentation in advocacy of those views. Inasmuch as you have asserted your credentials as a professional academic, you may wish to consider that both the quality of reasoning which underlies the historical and historiographic arguments you present and the mode in which you advocate those arguments reflects, not solely on you as an individual, but also on multiple institutions with which you have been or continue to be affiliated.
You should also reflect on another reality -- there are a great many practitioners of aikido and readers of this board who both have advanced academic training which included basic methodology courses of one kind or another -- whether humanist, social scientific, technological, or scientific. They will have their own, no less professionally or formally informed, views about your method. And even in the absence of such formal methodology, there is always bricolage and tact. On that last, Terry had quite a bit to say about tact, and as he noted when he taught a seminar at Bond Street -- at a time when his health was not good and he knew these would be his last classes at his old dojo -- he said that "everything I know about tact was hard-won, (at which point the room erupted in knowing laughter) so I commend it to your attention."
And echoing that observation, in all of its particulars, I close.