Before answering your question, I would like to see a comparative chart between junk bonds and other similar maturity bonds, both corporate and government. I suspect there is some correlation, but do not know any symbols for junk bonds.
My guess is that even junk bonds tend to trade on rate movements plus a relative "safe haven" thesis, although I realize that is not always the case. Still, the idea that even junk bonds represent somewhat of a better "safe haven" than stocks in a bear market is reasonable and that would go a long way to explain strength in the sector.
I would not see strength there as a prediction of a strong economy.