The English language has tried its hardest to get rid of accent marks by allowing vowel sounds to be altered through the use of things like silent vowels (e.g. a silent E on the end of "bar" changes the pronunciation of the A sound in "bare"), but knowing why they exist is handy for when you encounter loan-words from other languages like French and Greek. For example, in an English reading, the acute accent turns the neutral or silent reading of E into a long A sound. I don't know how it works for other languages, but that's what it does for English marking.
One of our schticks on the podcast is that we generally read what's written as it's been spelled, and since "agape" is its own word in English, Lemon did the same thing I would have done, even knowing what "agapé" is.
(Unless the accent mark actually was in the text and Lemon didn't read it right, in which case he was totally wrong to do that and shame on him!)