That's not necessarily true, a large part of it is hormonal response which varies depending on the amount of weight used, how many reps and how many sets. If you don't take in as much calories as usual and you try lifting weights it's most likely going to be detrimental to your body.
Reread my post - I was very careful to put the word "primarily" into the sentence. I also purposely left out the volume of work, tonnage, hormonal responses, amount of rest, timing of nutrition etc as the key part of bulking is nutrition - if you are not eating enough calories to bulk up, it is irrelevant what exercise you do - you will not bulk up to a level that is going to impinge on one's speed, or make them too "bulky". The general point that I was trying to make, without over complicating things too much was that a set of bench presses isn't going to turn you into Ronnie Coleman. Also, at no point have I recommended that the guy reduces his calories and implement a weight lifting programme, so you don't need to tell me that this will be detrimental to his health - I made no reference to any such thing, so you are on a completely different wavelength to me on that one buddy. If you also refer to my earlier post... You will notice that I am not advocating that the guy doesn't do any weights - I am suggesting that he if he trains in the correct manner, he will see results.
Buddy get back to the gym for boxing and start training hard... see how that goes then your coach there can give you some advise on your weakness.. Being Weights or strenght or what ever.. I can't bench press f all, but people dont push me around in wrestling or boxing (much) ..
to add a weight lifting routine to your program is your choice to do. It'll get you toned up good and get you alot stronger. But you also need to make sure your stretching regularly. Keep loose. If you stay flexible, you'll have better extension of your punches, which will make a more powerfull punch. When you do a weight lifting program, don't just work on one area. You do that for a year or so and you'll end up looking pretty goofy. Keep your routine to a full body work out. Start off with 3 days a week, full body work outs, light stretch during and after the work out, mabye even some sparring afterwords to help losen things up. Then on off days, you work more on endurance, hitting the mitts, bags and running. Get confertable doing that, then do your running 6 days a week in the morning, and you weight training and boxing in the evening.