Continuations after await on UI thread - concurrency data races

Continuations after await on UI thread - concurrency data races

Imagine that I have a button click event handler like:
public async void btn_Click(...)
{
await longRunningOperationAsync();
x += 2;
}
public async void btn2_Click(...)
{
await longRunningOperationAsync();
x += 3;
}
If the user clicks btn and immediately clicks btn2 just after, does it
cause data races? The statements after await will be executed concurrently
(e.g. preemption) in single thread (UI), right?
However, I have read this in that website: "all of your code is running in
the UI thread, so you don't have the issues with UI updates. In addition,
none of your code is running concurrently, which eliminates the data
integrity issues (deadlocks, race conditions) typically associated with
concurrency."
http://www.techrepublic.com/blog/software-engineer/why-net-developers-should-check-out-the-await-system/
I basically did not understand what happens.