The problem with looking at photos is male guinea pigs have an open inguinal ring so they can draw the testicles up quite high towards the abdomen if they so desire. I had one boar who would pull them in any time I picked them up but when lounging about they were obviously there. If I felt him even with them drawn up I could find them if I tried but from looking alone you could have sworn he was neutered. Your best bet is to physically feel him, if you have one that is confirmed in tact feel him so you can compare what you should be feeling for. They will feel quite firm. I have a neutered boar and when I feel him vs an in tact male it is very obvious he does indeed have nothing there.