ACL reconstruction, popping sound during foam rolling

Hey, please take the time to read this and help me :(
I am currently 5 and a half weeks post ACL surgery. I had a hamstring graft.
My rehab is going good, I am performing bodyweight squats fine, doing leg press fine, my hamstrings have been tight and the sorest part of the recovery process so far, especially the stringy part of the hamstring (when you tense the hamstring on the inside of the leg that stringy ligament that goes from hamstring to back of the knee) sorry for vague discription not sure of the names.. and I have had a hard time trying to get the leg 100% straight when standing up (can do it but feels like a tight stretch on back of knee)
Anyway, My physio has instructed me to use a foam roller at the end of my physio sessions as part of my recovery.
Today I was performing a simple foam roll on my operative legs hamstring when I felt and heard a ‘pop’ on back inside of my knee about a fingers length up. I immediately stopped.
It initially felt relieving as my hamstring tendons around this area have been tight, I got up and walked around and seam to walk fine, I performed some squats after this to test the area and it felt better now than what it did before the pop during the physio session. I called my physio and she told me that it could’ve been a ‘release’ and reassured me that I didn’t re-tear my graft as I wasn’t in any pain and she said ‘you would know if you re tore it you would be in a lot of pain’. I came home and researched it and found on the internet that some other people have had this problem at about the 6 month mark when running and they have been told and put it down as scar tissue popping. I iced it and have used a compression bandage for rest of afternoon just to be safe.
As it has cooled down it has stiffened up a little bit, I can still walk around and feel like my Knee is sturdy (no difference to my walking now that it has popped ). However Before the pop i couldn’t straighten the knee 100%, when I tried too I could feel tension and stiffness on the back of the knee/ lower inner hamstring tendon but my now it feels good, feels like it was before I injured the knee, can straighten the leg and doesn’t hurt at all just like I can on my other good leg.
Tonight before bed I lay down on my stomach to perform a few lying hamstring curls and can’t do them, it hurts, i also now can’t perform heal presses or hamstring bridges without feeling discomfort exactly where the pop was felt.
-Can you explain what the pop was?
-Have I retore the graft ?
-Why does it feel as though it’s “free’d” up now that it has popped ?
- Is popping scar tissue a thing? And if it is, is it normal for it to be stiff and sore after the release.