No it's not, sometimes my penis is just bigger for w/e reason, so it might cause a bigger bulge for a while. When I'm working out or playing any sport it shrinks big time (prob to protect itself lol) but then if I get a boner later on it might stay semi-hard or a bit less than that, sometimes the balls seem bigger and hang lower too so depending on the pants this can cause the bulge to be bigger as well.
So the short answer is no, the bulge doesn't always mean he's big, it could just be the how the "package" is placed in his pants and shorts and how big his penis is at that moment (for w/e reason, it changes size throughout the day)
I have a huge bulge but not a huge member, I am larger than average and am a shower and wear boxers. It hangs down my right leg and you can see it no matter what pants I wear. So if there is a bulge it's there for a reason. Unless of course they're stuffing. Lol
Most of the time your not even seeing anything but the jean or dress pant fold caused by the position/zipper/button. Not to mention temperature or adrenalin, or anything like that; could effect a guys size. Its also fairly different from flaccid to erect. Some grow a lot, some grow a little, some barely even grow. So no seeing a huge bulge in a guys pants does not = big penis or the equivalent to what's inside there, because pants do add padding and make it look thicker and a bit longer than it really is. Tho, I don't even know why you would ask this question other than you are curious and want a boyfriend with a big d*** and therefor, would be lying about your preference, otherwise you wouldn't have mentioned that fact or worded the question the way you did ... just saying.
well I been with my share of guys ,some men are huge some aren't ,but its been my exsprence when you see a big bluge either it is really large or as some guys I know they get excited when they see us , caint help but notice there winkys sticking out all huge asking for some attenion ,lets just hope its not a sock I knew a guy hedid that in high school lol
you can't really tell with the pants unless he actually has an erection and he is wearing a certain kind of pants. with jeans you can't really tell. with suit pants it may be a bit more obvious but he would probably have to be sitting in a certain position with his legs spread to really tell.