Your two anecdotes do seem rude, however I would personally have asked the same thing, but in a different way, like "We could continue in English if you want" with probably a slight incentive in my tone to actually switch to English (sorry if I also appear a bit rude). Or Maybe I will just reply to your every question in English.
A native English speaker is blessed, English has become the de facto lingua franca of the World which means learning a foreign language generally is a luxury. For everybody else, it's more of a necessity, and you tend to be exposed to English in your everyday life, at least to some degree (films, tv shows, technical documentation, meetings if you work within an international team), so chances are the person you are talking to is actually more fluent in English that you are in French (and it's also valid for any other language).
It also means it's somewhat harder to actually learn a foreign language as a native English. As a personal experience, one of my colleagues is American, but wants to settle in France, so he is trying to learn French, and sometimes, we actually start speaking in French, but after one or two minutes, we switch to English. I just see my colleague struggling and I know the conversation would be easier in English. I feel a little guilty about it.
Lastly, but a bit out of topic, there might be some small cultural differences. Just to illustrate, In an American restaurant, the waiter will ask you if everything is ok at least once or twice during the course of the meal, in a French restaurant, he will take your order and leave you alone until you finish eating your dish (and then ask you if you want a desert, a coffee or the bill).