Don't worry, its unlikely that a creator like this with a huge playerbase would put a random trojan into this game. And might as well enjoy the game cuz if there is a virus, it would've already activated.
I can't really think of a reasonable explanation for this but its most likely safe because the VN "echo" had the same warning but was trustworthy because it was made from the same people that made Adastra. And some engines just use commands and stuff to run the game or to extract the data from saves and stuff.
Short Answer: Most likely your fine because of the magnitude of players that have downloaded this and none have reported similar issues, and if your still suspicious you can do a deep virus scan from antivirus companies (would recommend Bitdefender - the free version - but you can use any).