My intuition for this is people buying bonds leads to excess demand of bonds due to which price of bonds increases as price of bonds ( given the return of bond is fixed the price of bonds is inversely related to interest rate) hence r decreases.

Now in the assetsmarket there are two types of assets moneytary and non moneytary if the return of moneytary asset goes up you switch from nonmoneytary to moneytary assets and viceversa which is exactly the case her if price of bond increases the rate of return on bond is more hence people take out their money and put it into bonds hence there is Excess supply of money due to which real interest rate falls.