The guy you were talking about knows nothing about brakes, braking and how braking works on a bicycle. He's got lots and lots of company. Thankfully, there are people who know a lot about bicycles and bicycle brakes. One is David Gordan Wilson who wrote "Bicycling Science" which is about a nerdy a bicycle book as you'll find but worth reading if you want to know the physics of why we do what we do on a bike. The book is a bit dated...it was published in 1974...but, thankfully, the physics hasn't changed since then.

Let's start with the idea that most of your braking is done on the front brake. Knobster is right, it is. When you brake on a bike, the weight of the bike and, more importantly, the rider, gets transfer forward over the front wheel. Even on a bike that brakes with only the rear wheel, this transfer is evident. If you've ever ridden a coaster brake equipped bike, you will soon find that the bike can be skidded to your heart's delight. That skid is the rear wheel wanting to lose on contact with the ground as the weight of the rider is pushed forward over the front axle. You can't endo a coaster brake bike because you lose all what little braking power you have when the rear wheel leaves the ground but you can certainly skid it very well. You can do the same with a bike that have brakes front and rear by simply using the rear brake. If you throw in a little hip check, you can slid the bike to a fantastic sideways stop.

When you have brakes on both wheels, you are in a different situation. Since you can continue to brake after the rear wheel lifts, it is possible to endo. In fact the point of maximum deceleration comes at the point just before the bike pitches the rider over the handlebars, i.e. an nose wheelie. This is the point of maximum possible deceleration and is a mathematical oddity. Practically, you don't really want to find yourself in that situation every time you come to a stop for the simple reason that if you do a nose wheelie, you are riding a poorly designed unicycle.

You should still have the larger more powerful brake in the front of the vehicle (any vehicle) because that's where most of the braking occurs even if you aren't doing a nose wheelie. In a regular braking situation, i.e. with the rider seated on the saddle in a "normal" position, you can develop about 0.5g of deceleration ('g' is the deceleration due to gravity). 0.4g or about 80% of the power comes from the front brake. The rear brake provides 0.1g or 20% of the braking power. If you remain in that position, and start to lift the rear wheel, the amount that comes from the rear decreases and the amount that comes from the front increase. At the maximum possible deceleration point, the rider is about the spin around the center of gravity right above the axle and smash into the ground. Not a good place to be.

You can get more deceleration out of your bike than 0.5g, however. If you shift your weight rearward and down, you can double it while also decreasing the change of going over the bars. The amount of the shift of the center of gravity is tiny. A movement of your body back about 4" and down about 2" is all that's needed. It's a practice that every mountain biker learns on their first day of riding. If you actually want to do a nose wheelie (or a cool skidding stop), shift your weight forward and the amount of deceleration you can attain before being thrown over the bars goes down.

The reason you use less front in bad conditions is because the front wheel could slide on slick pavement. A rear wheel sliding is easily dealt with and you can usually recover from that. If the front wheel slides, you lose all control of that wheel and probably can't keep from crashing.

Braking on a bike is complicated. Most people don't know anything about it although they may do it all the time. Usually, they find out what they don't know only at the point where they need to know it. The guy you are referencing is one of those people.