>> Conventionally, the formation of chemical bonds is due to a decrease in potential energy (PE), often accompanied by small increases in vibrational zero point energy (ZPE). In principle, this basic mechanism can be completely reversed, wherein chemical bonds may even be formed by an increase in PE if there is a sufficiently compensating decrease in vibrational ZPE, giving rise to what has been coined “vibrational bonding” of molecules stabilized at saddle-point barriers on a potential energy surface (PES), far away from potential minima.
When two normal molecules, with electrons, are close, they can form different kind of bonds. The weakest bond is the "van der Waals" bond. It's caused because the electrons of the molecules change their position slightly due to the presence of the other molecule.
In this experiment they only replace the electron of a hydrogen atom by a muon. The muons have much more mass than the electrons, so the radius of the orbit is much smaller. (They are quantum particles, so they don't have orbits, but please forgive this technical detail.) As the orbits are smaller, the displacement caused by the other molecule is smaller, so the van der Walls force is smaller.
In the normal (electron) case the van der Walls force cause the formation of the intermediate molecule. In this case (muon) the van der Waals forcé is so weak that other effects are more important.
[I left out the part about zero point energy. It's also interesting but this explanation is becoming larger than the article :) .]