Manual stretching aches

Is anyone else experiencing slight aches after stretching a bit harder? Like I remember one time before I was doing PE I randomly stretched it a bit harder (I’m talking about medium pull, I really didn’t pull it hard) and the next morning I woke up with aches that stopped after I got out of bed.

Yesterday I did stretches and I pulled just a bit harder than normal and after that I got slight aches again above my penis. These aches occured today too when I make some moves, they are very weak, but it still points that something is wrong. By tomorrow they should be gone I think.

Now, the question is why… I have a theory that whatever is located above my penis (some ligaments or something?) is a bit shorter because all my life I held my penis poiting up in my udnerwear, my erections point up etc… and that this part is not stretched enough and it reacts to these stretches… I was also like 10-20% hard (like literally just started to get blood inside) while I was doing some stretches and that also seems to affect it.

The videos on this forum show a half hard guy pulling his penis like crazy, now can someone explain to me how that is safe? Do you have any tips how ti improve safety of stretching?