We did have a confirmation that mobile is counted (however I'm unsure if it requires you to login into your Steam account to be counted, or whether they count anonymous users too).Yeah, you may be right. The SteamDB folks suspect mobile players are included, since said version also requires a Steam account to play and the game supports cross-play, but I don't think we have hard confirmation on that.
Pavel Djundik on Twitter
“See this player drop on today's @DotaUnderlords charts? That was a change Valve did to count mobile players separately and later fixed or reverted it. That tells us around 30-40% players are on mobile (only these that logged into Steam).”
twitter.com