Do wireless amplifiers work in both directions?
No. They are the same. Likely they don't want you to use a USB network adapter for other design reasons (like how most of them don't have the RF link that you need to attach to this board, they instead have internal antenna and their own compensation networks).
Yes. Technically speaking an RF amplifier only works in one direction. This board likely either uses two amplifiers which are time division multiplexed or has only one amplifier and a time division multiplex back to the receiver without any amplification. (If they are fancy and thoughtful, they might even be using an active isolator).
As I described above, the incoming signal is routed to a different amplifier, "facing" the other way. This way neither amplifier can drive the other (amplifiers go poof), nor can the other amplifier use the antenna at that time (no garbled signals from talking and listening at the same time on an antenna that might not be perfect).


This is all very abstract and high level of explanation and the exact details aren't perfect. It's not my design. I've never seen this before in my life. I don't generally trust Chinese designs unless they release a parts list. The board is also missing its RF connectors, which makes me dislike it even more. (Honestly, it's a bit shady to have an RF board without any RF connectors. Like I can literally see the solder points but they are so obviously designed for a side mount standard coaxial screw that I wonder why they're not there.)