This definitely fishy.
1. You are absolutely right. The email client doesn't automatically compress files. You can get prompted if you want the compress it, particularly when sending from your phone. It will not, even if you do elect to compress the size of the file, rename it. Prosecutor definitely came across as dishonest at best.
2. Why the fuck is the prosecutor sending evidence via his personal fucking gmail account? That's just stupid.
3. Isn't it the prosecutor's responsibility to ensure that the defense gets the evidence?
Then to sit there and say that they had every opportunity to object to it is flat wrong. How can they possibly object to it when the file that they were given was not the file that was entered into evidence? "Oh, they could have had an expert look at it and see that it had been compressed." None of them know anything about this stuff and it's aggravating.