That hypothesis seems less likely and more complicated than the sentry one.

Scanning wildcards for well-known subdomains seems both quite specific and rather costly for unclear benefits.

Bots regularly try to bruteforce domain paths to find things like /wp-admin, bruteforcing subdomains isn't any more complicated

> Bots regularly try to bruteforce domain paths to find things like /wp-admin

Sure, when WordPress powers 45% of all websites, your odds to reach something by hitting /wp-admin are high.

The space of all the possible unknown subdomains is way bigger than a few well known paths you can attack.