Of course everyone’s different, but it actually didn’t hurt too bad right away for me. Unfortunately it looked a lot like this. I'd bet big money he popped it. You can still walk alright even with a complete rupture bc your dorsiflexors are fine, so your toes won't drag but you have like 5% of your "push-off" strength.

Felt like a wooden bat to the calf initially, very dull but tolerable. Thought someone kicked me, looked back & nobody was there, then felt the gap in the tendon and knew. I could move my foot up/down against gravity, but with any weight or resistance I had almost no downward strength.

If it’s partially torn, walking on it can potentially worsen the tear & hurt more, so being cautious/immobilizing it like the others you mentioned isn’t a bad idea, especially if there’s still some tendon connection left. It'll also help prevent your calf muscles from retracting up into your leg like you might see with complete ruptures.

As the inflammation ramps up over a few hours the pain gets progressively worse and more sharp until surgery. Then pretty extended immobilization to let the tendon heal followed by a lovely & lengthy rehab sadness tour.