Should I reject a specific historic fact and not include it in my work? Advice needed on reliability of source
It’s useful to consider the potential harm in making a wrong decision of either kind here. If you don’t mention the historical anecdote in your paper but it’s actually true, readers won’t miss out on much, and in any case won’t be actively misled — after all, you’re not claiming the anecdote never happened, you’re just not mentioning it at all. Those readers who want to learn about Boris Belousov’s life can still go and look for additional credible information about him. Presumably they will run into this anecdote. And your paper is in any case a science paper and not a history paper, so no one can accuse you of depriving anyone of critical information.

By contrast, if you mention the anecdote but it’s not historically substantiated, you do a great harm to your readers and to Belousov himself by helping to perpetuate a fallacious myth about him. The harm caused by this type of mistake is much greater in my opinion.

Another thing to consider is the credibility of the source and the level of scholarship that backs up the paper’s contents. The author of the paper you linked appears to be a high school student, and the journal it’s published in is a journal with low standards whose specific mission is to publish the work of budding researchers who don’t yet have a bachelor’s degree. The author doesn’t give a specific reference for the source of this anecdote, making it unverifiable. That’s not good practice, and it may reflect poorly on you to cite such a source without warning your readers about its potential lack of credibility if you rely on it for any information you were not able to verify from other sources.