Slack and Discord both do this as you type, on desktop at least. (Can’t verify Slack on iOS, Discord does not on iOS but this is an iOS thing, not a Discord thing.)
I’d be a bit surprised if it was entirely alien, since using * for emphasis around words isn’t that uncommon, _ is not commonly typed in general, etc.
(Could be worse. Could be MediaWiki syntax which uses two single quotes either side of text for italics, and three single quotes either side for bold (so bold and italics is 5 single quotes either side of your text)
Another data point: one community I manage, not XF (and likely never to be unless I port a metric buttload of custom code), but it has people who write in Pages on iOS, on Word, and in one case in Notepad++, all doing bbcode inline in their posts and copy it in after. Writerly types are weird.
