Probably because the Soviets did a lot of copying when it comes to western technology... Rumour has it the KGB has a complete set of blueprints for most American aircraft up to the late 80s and even a set for the USS Nimitz!
I'm always somewhat circumspect about such 'rumours'. The TU - 160 is a larger and quite different beast, compared to the B - 1. Aside that, surely an (assumed) approximately similar understanding of aerodynamics will often produce similar 'shapes' when aircraft are designed for similar mission parameters.
Who knows...
Mind you, those odd looking wing glove / fence thingies on the '160 aren't sported by the B - 1. What are they all about? Looks like something of a fudge to me.