Example question from studyhub

Example Nominal and Real GDP
The nominal GDP of Ayeland is $5.0 billion for 20X1. In 20X2, Ayeland’s nominal GDP is measured at $5.5 billion. The inflation rate for 20X2 was 6%.

What was the real GDP growth of Ayeland in 20X2?

Answer:
Ayeland’s 20X2 nominal GDP (including inflation effects) is $5.5 billion, an increase of 10% from 20X1.

However, since the inflation rate was 6% for the period, Ayeland’s real GDP is calculated as follows:

Real GDP

= Nominal GDP / (1 + inflation rate %)

= $5.5 billion / (1 + 6%)

= $5.5 billion / (1.06)

= $5.19 billion

The summary of Ayeland’s GDP growth is as follows:

Nominal GDP Real GDP
Year 20X1 $5.00 billion $5.00 billion
Year 20X2 $5.50 billion $5.19 billion
Growth % 10.0% 3.8%
([5.5 / 5.00] – 1) ([5.19 / 5.00] -1)

I understand the calculation and formula but I don’t get why they have calculated Price index of Real GDP by comparing current year’s Real GDP (without inflation effect) with last year’s Nominal GDP (including inflation effect). Isn’t the 3.8% an unreliable measure as the last year’s nominal GDP includes inflation effect in itself? Should they have not compared like with like, in this case Real GDP of current year with last year’s Real GDP instead of Nominal GDP?