Yes, that is true. Insurance adjusters are on the look-out for any indication that you are not as hurt as you say you are. So posting anything at all that shows you happy or engaged in activities that would call into question the legitimacy of your injuries is a big mistake. You might not even think that what you are posting could possibly be used against you, but you would be surprised at how anything can be twisted in a court of law. So be safe and stay away from social media during the pendency of your case.