He could’ve been actively looking! It’s very common to look at blogs and opeds and literary magazines (short form writing) to ‘scout’ for book potential. most agents/agencies delegate that kind of work to agency assistants (it’s also a good way to train them to spot good writing etc.), and some agents/agencies scout more than others, and based on my anecdata I’d say SFF agents do it more because there’s a lot of short form SFF writing outlets. “Stumbling over by chance” is a better story as it implies a lot of things like discovering diamonds in the rough/elevating somebody from obscurity/etc all of which can be useful marketing tools - not that it’s not true, he very well might have come across it by accident. Either option is equally likely, and I should probably make clear, value neutral.

Related, I think if one has an interest in something or other, intentionally going into online rabbit holes can sometimes lead to a lot of interesting stuff. I can’t count the number of times I’ve wound up on somebody’s blog because I started on Wikipedia idly looking up something I was curious about…