I still don’t see the problem. Witnesses prepare for grand jury testimony all the time. Since they are unable to have legal counsel with them during the questioning process, they better have their act together. He’s had plenty of time to think about how he’d explain this w/or w/o lawyer prep.
Regardless, I would have advised my client to speak naturally, rather than contriving a phrase that includes “five year old” and “Hulk Hogan.” “His arms were huge compared to mine, like a weightlifter or football player.”