I'm not sure what Popper's motivation for saying that was, but I've read a bit of Heidegger and I felt the same way afterward.
Here's another Popper quote on Heidegger. No points for guessing how Popper took this (as is clear from the surrounding context):
"'I did not understand a word; but I know: this is philosophy' was the deep conviction of a highly gifted young physicist after he had heard Martin Heidegger speak."
--"The Unknown Xenophanes", The World of Parmenides, Karl Popper
Take off every 'quote'! You know what you doing. For great insight. Move 'quote'.
And if you don't: