One has to do with language. French people are taught to be proud of their language and do not always like it when people make no attempt to speak it.
And, although most younger people now have had at least a few years of English in school, the standard of spoken English among older people is not generally high so replying to English with French could be construed as not liking outsiders but might simply be a lack of language skills, just the same as the English-speaker is showing in this example!
Another point to make is the notion of service in French restaurants and cafés. Waiters are not, like elsewhere, casual workers but, often, full professionals offering efficient service albeit with, sometimes, no small talk.
Many have undergone two years of formal training – they can hold one of five different qualifications for waiters – and there are specialist courses at écoles d’hôtellerie, which are usually privately run. There is also on-the-job training without formal qualification.
It is a serious job and good waiters can earn much more than the minimum wage and are treated with respect.
Looked at in a different way, you can say the French are outstandingly social and generous with 23 million people (in a country of 66.9m) being part of a charity or association that covers everything from sport and culture to food banks and other social goals often involving foreign causes. Latest figures (2016) show there are 12.7m volunteers among those 23m so that is a lot of people working together for the common good.