Syd Barrett with The Beatles

Syd was not on this or any other Beatles recording, the group did visit the studio when they were recording Pepper (as mentioned they were next door recording piper) and were very quiet and in awe of the Beatles.

How anyone could mistake Lennons vocals is beyond me, after all, apart from when they gave songs to Ringo, they only sung the songs they had the predominent input into (apart from covers natch).