Those were the early days of radio, as in "Let there be light" kind of early.

Very few people could even build a receiver, much less tune it.

Nah. He just did a broad spectrum broadcast which any receiver in the area would pick up. Today, it'd probably be illegal. Tom Scott made a video about it, and mentioned that. https://www.youtube.com/watch?v=sP2qqMegNKA