I'm a foreign traveler in the us. My us health insurance covers only $5000 for surgeries. Isn't that too little? Wouldn't emergency surgery cost more?

Yes. In my opinion. That is not an amount that would cover any significant problem. One big expense that you might want to consider is an emergency transport track to a us hospital. That alone can be 10 thousand dollars or more.
Yes. You're correct. As a traveller i would assume we are talking about an emergency situation, and when combining surgeon, anesthesia, and hospital costs, the total would be greater than $5, 000. However make sure it's not just the surgeon's fees which would probably be less than $5000. Also sometimes my patients confuse the deductable (the part you pay) with the coverage amount (what insurance pays).
Travel. Travel accidents do happen, but unlikely injury is more significant then fracture, $5000 should be ok for surgeon's fees. If you have catastrophic event your coverage should be up to $100 000. Chances are very low, but it is your choice how much coverage and risk you can accept.