[EDIT 2023 Nov: ] As per my uderstanding, there are multiple ways to interpret the tax treaty between USA and Sri Lanka. Following is my advice on what to do.
There are a bunch of documents that are relevant to this issue. I strongly suggest you read them and fill the tax forms. If you are unable to interpret them by yourself, please take them to CPA. Sometimes, your university's international student office have a person to help you with this. The documents are as follows.