Hello Zdenek
Yes, that is correct. Only outgoing traffic, that is traffic from R1 to R2/R3 is load balanced. There is no way to load balance incoming traffic from the point of view of R1. In other words, there is no configuration within R1 that can be made in order to cause incoming traffic to take two routes to get to R1. Having said that, it is possible to configure load balancing on the side of the other AS and configure load balancing for outgoing traffic from the point of view of the other AS.
I hope this has been helpful!
Laz