For those learning: the voice pronounces llyn incorrectly -- it pronounces it like llun "picture", i.e. the voice uses a long ŷ sound.
It should instead be a short sound as in gwyn "white" (pretty much like the vowel in English "thin").
If you have access to Gweiadur, listen to the recording in the entry for llyn.
Yeah, this is a shame because learners tend to mix up these words anyway.
short vowel: llyn "lake" N: /ɬɨ̞n/, S: /ɬɪn/
long vowel: llun "picture" N: /ɬɨːn/, S: /ɬiːn/
long vowel: llyn "Llŷn" (area of NW Wales) N: /ɬɨːn/, S: /ɬiːn/
There's also the word:
long vowel: llin "flax" N/S: /ɬiːn/