Mathieu is under a lot of pressure, and he is trying to justify his salary to play for the money he COULD earn next season.
This is not the 1st time Mathieu has gotten into "Twitter fights", he had a few with old friends in New Orleans a few years ago, IIRC.
As the the "blown" assignment against Marquise Goodwin? I thought it was Patrick Peterson all along. Peterson likes to let the receiver get a little distance and then with the ball in the air, Peterson catches up to the receiver to make a play. He has done this a lot in his career.
One problem. Marquise Goodwin is one of the few players faster than Patrick Peterson, thus Peterson could not catch up to him.
Marquise Goodwin is the same player that ran down Peterson when Peterson tried to return his fumble recovery.
Mathieu has to get thicker skin and worry more about making more plays (like the strip for a fumble), and less about what social media thinks.
Cause right now ? The only way he stays on the team next year is a pay cut.