Normally, I would go for what you have told. But since the preference is room 2 over room 3, and we are to find a logic for that preference, my take would be -
What can we say about the strength of people attending?
It would surely be more than 8 and at the most 12 ( reason why room 1 is first preference).
Preferences : He surely would prefer a VC and Projector, and 2 and 3 have the same status.
Difference :
1. The difference is room 2 has 12 and room 3 has a max capacity of 20. Now, we know he expects at the most 12, so would a room with larger capacity than what is required preferable. If there is no Video Conferencing, he may want the best possible use of tele conferencing and smaller room may be a better choice.
2. Availability of room 2 on a later day. It is mentioned that he prefers the conference earlier in the week. Note he is not looking for the earliest in week. Maybe both Tuesday and Wednesday would fit in when we speak of earlier in the week.