Neville: "All Muggle"?

[charme]

No: HPFGUIDX 121521

I have, like many of you I'm sure, been rereading the series  and I've found 
something interesting in SS/PS that I overlooked before.  I can't make out 
if it's mistake, or if something thought-provoking is afoot.

SS/PS, US: "Well, my gran brought me up and she's a witch," said Neville, 
"but the family thought I was all- Muggle for ages.

All Muggle? Is this the same in the UK editions? Doesn't DD say that Neville 
is pureblood in OoP when explaining the prophecy to Harry?  Donning my 
spyglass and usual suspicious nature, why would Neville (a supposed 
pureblood) describe his grandmother and Great Uncle Algie as thinking he was 
"all Muggle?"

charme