The use of "better" in this context is in fact subjective, based on having different priorities. When you say "you could do better", you apparently mean "you could clear this faster", because your priority is to clear as fast (or as smoothly) as possible. For them however, the priority is not to clear as fast as possible, but to enjoy the content more, so doing "better" for them would be not to have the mechanics spoiled in advance as the thrill of discovery is evidently important to that enjoyment.
I echo the sentiment of others here however that the way in which it was handled was not acceptable. If I had been in their place, I would have politely declined an explanation and that would have been the end of it.