Writer At Work
With the phrase...
"...his eyes flashed anger for a moment”
...you've stumbled upon "The Writer at Work".
Which means that the writer has interrupted your reader's reverie by choosing a phrase that cannot be "seen". It jars you from the story itself and is intrusive.
This is why writers often repeat the old adage, "Show don't tell."
This "eyes flashed with anger" has become a cliché, not a descriptive showing of what is actually happening. It is a shortcut that a writer has used (and now many writers copy) to tell the reader that "The character was angry but is trying to hide it."
It is far better to show the action as if you saw it happen on a movie screen and then wrote it down. The best way to do that is:
1) determine what you want to show - in this case we want to show a character becoming angry but attempting to hide it from one or more other characters.
2) imagine how an actor might portray it on screen in a movie
Now, how about this.
His boss said, "Well, if you weren't so stupid, maybe you wouldn't
have lost the sale."
Wesley turned his face away from his boss and
stared at the cubicle wall. He held his breath and gritted his teeth.
Then he turned slowly back around. "I'll do better next time, boss."
This is showing the anger happen, not telling the reader what they should think is happening. It is far more powerful because the viewer/reader gets to decide what is happening.