Usually, the Lord simply blesses what we set our hand to do. The resources were totally inadequate to meet the need in this instance, but when the Lord blessed it, there was more than enough.
Jesus didn't just teach the disciples, but He trained them also. He was constantly trying to involve them in these miracles. Just a matter of days later, He again asked His disciples what they could do to feed the multitude of four thousand men. It was like He was saying "You missed this question when I asked you how we could feed the five thousand men. Now, here are less people and more food. What would you suggest this time?"
Instead of remembering the previous miracle, they acted like they had never seen Jesus feed the multitude and they looked at their own resources again (Matthew 15:32; Mk. 8:1). We all often try everything we can do first and forget God's supernatural power until all we can do is pray. Many people have missed their miracle because they never took that first step of faith and used what they had.
This young lad was certainly credited with part of this miracle for offering what he had. When in need, we should seek God's direction for something to set our hand to, and then trust Him to bless it and multiply the results of our work.