That bold part is reported in news, not my reply. PIBs usually offer more yields than MTBs being long term assets.
@Topic
Simple price yield (interest) relationship. If i buy a high yield fixed income asset today -i.e. a PIB with a coupon of 7%- and market interest rate is the same as the return of the asset, the asset will be priced at par. However, if I expect that the the market interest rate tomorrow is going to be reduced to 6%, then my asset having 7% of return will be priced at a premium tomorrow (because the par asset will then by a PIB having 6% yield).
A simple pricing formula goes PV=Sum[C/(1+i)^n]+P/(1+i)^n (Where C denotes coupons and P is principal face value)
Now let us consider an example
Suppose I have a PIB of face value 100 offering 10 Rs annualy having 2 year maturity
now given the market interest rate (or yield) is 10%
PV=10/1.10+10/1.10^2+100/1.10^2=100
Now lets say that the market yield is now 9%
The PV will increase to 101.75911 resulting in a gain of 1.75911 Rs.
That's why banks are heavily investing in PIBs