Only if he thinks he can only weakly affect outcomes, or exert large amount of control as the evidence starts coming in.
Remember he's playing an iterated game. So, if we assume that right now he has very little information about which area is the most important to invest in or which areas are most likely to produce the best return, playing a wider distribution in order to gain information in order maximize the utility of later rounds of donations/investments seems rational.
http://blakemasters.tumblr.com/post/24464587112/peter-thiels-cs183-startup-class-17-deep-thought
Some perspectives on AI risk that might be interesting. Peter is (the primary?) donor for SI, and an investor in AGI startup Vicarious Systems.