No. What it means is that your brother was smart enough to avoid any websites or downloads that potentially carried any virus files. AVG could have been said to have done a good job if it actually squashed any viruses your brother actually received, and when switching to Kaspersky, the new AV didn't find any more.
Thing about virus, malware, Trojans is that AV is totally reliant on actual abuse. Someone gets a virus, it gets tagged as a possible by heuristics, sent to the company, the company reverse engineers it, adds it to the list and then puts it out in updates. It's entirely possible for AVG to figure out a fix for a virus, and not any other company for a while, it's dependent solely on the amount of users and the spread of the virus. If a Kaspersky user never gets the virus, Kaspersky won't get the chance to make a fix. Or Norton or Panda etc.
What makes or breaks a good AV is the level of diagnosis of the heuristic program. If it's junk, you get a virus that's not quarantined, and then spread it to others, after it's damaged your software. If it's good, the virus gets quarantined, the company gets notified and you luck out.
Any AV can find a virus that's already labeled and known and squash it before it does damage, it's the unknown virus that's a problem. And there's very few original viruses, most are offshoots of others, mutations, and heuristics is pretty good at finding those too. Malware and Trojans are somewhat different as they are not software damaging, but performance affecting and much easier to code, being nothing more than a switch. Turn it on and everyone knows your secrets. Finding those is harder as the program has to recognize that switch for what it is, buried in software you agreed to add.