When the agent looks down (change camera angle with delta_pitch=90), all blocks become much smaller than usual. Is this an intended design or a bug?
That depends on the field-of-view of the player. You seem to be playing with the default 70 FOV (the lower picture), where as the recordings seem to be done in maximum 110 FOV (upper picture). This is based on quick round in vanilla Minecraft.
Yes, it does depend on the FOV! Thank you, Miffyli.