I honestly do not see how the two things are related. Spending 15€ once instead of 8€ once is not really a sign of anything. You can do that even as an unemployed person on Bürgergeld.

What is worrying about the German economy is also not the current inflation but the long term outlook: the energy prices that will never be competitive, the 20 years of technological lag within almost all industries due to lack of investment and extremely risk averse financial climate, and the ever aging population, which now Germans are starting to realize, won't be so easily solved by immigration, neither illegal nor legal.