No, the one-inside-a-circle symbol does not indicate a toggle between off and on, as this article "surmises".
Instead, it indicates stands by. This is off, but not fully off as a circle would suggest. It's nearly on. The symbol is great for that.
On a push button it means activate stand by or come back out of it (i.e., turn back on fully). Still fair enough.
Unfortunately, this knowledge has watered down over time. I've seen that symbol used more than once for a button that only turns on a device (never back to stand by). That's pretty much the opposite of its original meaning.
Instead, it indicates stands by. This is off, but not fully off as a circle would suggest. It's nearly on. The symbol is great for that.
On a push button it means activate stand by or come back out of it (i.e., turn back on fully). Still fair enough.
Unfortunately, this knowledge has watered down over time. I've seen that symbol used more than once for a button that only turns on a device (never back to stand by). That's pretty much the opposite of its original meaning.