I’ll echo the posters who have said that it can mean a lot of things. I recently posted an ad for my OTTB gelding. This horse is exactly the same personality if you ride him daily or give him a month off in the winter. He is just naturally exceptionally quiet and easy going. However, he is on the green side and generally sedentary even in turnout. He does best with a program to keep him moving, in decent shape, and to continue his education. I don’t take tons of lessons myself, but I have brought along every horse I have ever owned (yay having champagne taste on a beer budget!!!), so I have been able to create my own program, and would be comfortable with him going to a similar adult.
It’s not a warning about my “explosive horse”, it’s parameters I have set to make sure my horse is successful. With every person I have spoken to about him, I have described the “programs” I feel he would do best in. I don’t believe my horse would ever hurt someone, but I want him to maintain, and, if possible, increase his value. Being in a program will accomplish this.