It does look like it could possibly be a boar, have a feel just above the genitals. Male guinea pigs have a bone in their penis which can be felt as a firm line under the skin, if you press down just above where this line starts and roll your finger down the penis will pop out. Female guinea pigs will be soft and squishy above their genitals as they don't have a bone there, and if you roll your finger down nothing will happen.