There is an important factor at play in the bond market that isn't shown by looking only at historical returns. Bond returns consist of two things: the bond yield and any appreciation in price. Both of those factors are driven by interest rates. Higher interest rates mean higher yields (otherwise people would put their money in a saving account instead). And when rates are cut that helps bond prices, because existing bonds now have a higher rate than new bonds will.
For 30 years, this created a win-win situation in bonds. I say 30 years, because in 1981 interest rates were at a staggering 15%. This meant that bonds started at a high point, and that for the next few decades the Fed mostly cut interest rates, leading to steady increases in bond prices.
However, following the financial crisis, interest rates were cut to near zero (and in fact have negative real yields in many countries). So not only are yields low now, there is not much more cutting that can be done to improve bond prices. Instead, the only direction for interest rates is up, which should hurt bond prices. This is the essential reason why people have become so negative on bonds in recent years.
It is possible that bond prices could rise if there is higher demand for them, but it's worth remembering that the Fed and its counterparts are holding a lot of bonds on their balance sheets that they bought up during the last crisis that they will eventually want to unload. So there may be a lot of false demand in the market as it is.
I wouldn't freak out too much over a single article. Most financial predictions are wrong. I just posted it because it was an interesting topic for discussion, not because I am convinced it is going to come true.
