If the bidding is fair, why not?
Usually when proposals are evaluated, following aspects are assessed:
1 - Quality of Service/ Product
2 - Cost/ Price
3 - Post Acquisition Services and Warranties
4 - Previous Experience
5 - Adaptability
6 - Possibility of Establishing Local Servicing Centers/ Mechanical Workshops
Above is not an exhaustive list, but some very key aspects which are evaluated.
If China has beaten Japan on the above aspects, why not? China is running one of the largest (if not the largest) rail networks without any issues.