According to one Nepalese news site, Mr. Thapa apparently is under investigation for money laundering in Nepal. Note that Rastriya Swatantra Party's founding leader Ravi Lamichane is also accused of money laundering and now facing criminal trail in Nepal.

The news site writes. "Reports suggest that Thapa returned to the U.S. last week following an investigation into money laundering in Nepal."

- https://english.pardafas.com/rsp-central-member-mohan-thapa-arrested-in-the-u-s/

If this is true, it is fairly normal for government of any country to ask foreign government to arrest someone who is under criminal investigation if that individual escapes to that foreign country.

In Mr. Thapa's case, all KP Oli's government possibly did was inform the Trump Administration about someone under criminal investigation in Nepal possibly escaping to US to evade criminal prosecution in Nepal.