That account has been moderated in the group. He was probably hacked/infected. (Not the first time this has happened.)
EVERYONE: Whenever this happens, post a message in a new thread in the group (as you have done Stephen). We monitor the postings (not continuously... we have grand children! :>) and will spot it and take action. (Posting in the thread may not get our attention quickly unless it is extremely obvious.)
ALWAYS be careful about suspicious email (even from known associates... eventually everyone can be hacked). Remember that the spammers and hackers are ALWAYS ahead of any anti-virus/anti-malware software you have.
I personally use email rules to put all mail in my junk box (when not from a well known source). That disables the graphics, scripts... Also allows me to verify the name matches the email. (Sooooo many claiming to be from comcast the business but from private email addresses has been a theme recently for me.)
Best wishes,
Ed