OK, again I will tell you something you appear not to know. The bond world is a diverse as the stock world. High yield bonds which was one of the subjects of the post is most directly correlated to the stock not the bond market. High yield bonds, or "junk bond" depend on the capital markets to raise funds which cost the companies more in interest payments. The context is that the reach for yield is allowing companies with poor business models to continue in business a little longer. Historically high yield bonds do well at the the peak of the business cycle.
On the other hand, high quality bonds tend to attract capital in times of poor stock markets, and are more directly correlated to the interest rate market. Think of it this way, if I own a bond that pays 4% interest and five years later the market is 2%, since my bond pays more than the market, it has a higher value IF I SELL THE BOND. Conversely, if I own a bond that pays 4% interest and five years later the market is 6%, since my bond pays less than the market, it has a lower value IF I SELL THE BOND. IF I HOLD THE BOND TO MATURITY IN EITHER CASE I MAKE MY 4%
In regards to bonds being in bubble territory, the same could have been said about Japanese government bonds a decade ago, and it did not play out that way. There is an argument to be made that owning a ten year Treasury bond at 2.4% and holding it to maturity will be a better investment than buying the S&P 500 at 2,100.