What kinds of rewards were these that are not taxed?

Business travel is not taxable for the employee.

Okay, but how is that a reward? Maybe I wrongfully assumed we were talking about a money / material reward here.

If you consider going to a conference abroad like a mini-holiday with everything paid, and maybe even some fun activity, well, it can be seen as a reward.

Many big tech companies treat business trips as rewards. Fly business, live in a nice-ish hotel, get meals and taxi comped. It's a little vacation.

One of my early managers (based in Asia) saw his annual two-week business trip to the Bay Area as one of the most valuable perks of the job. He even brought his family along a few times (he paid for their travel obviously, but they probably shared his hotel rooms).

I got to spend a week in a nice hotel in an exciting foreign location with (by Swedish standards) fantastic weather for free.

Personally I also enjoyed some of the C++ talks, but I had no obligation to attend them.