United were reportedly interested in bringing Longstaff to Old Trafford during the transfer window.
The Red Devils were thought to be readying a bid of £25m for the midfielder but Newcastle wanted close to double that instead.
The move failed to materialise in the end and United signed Harry Maguire, Aaron Wan-Bissaka and Daniel James.
But Longstaff, who has impressed this season for Newcastle, has said he found it hard to not be distracted by all the transfer talk in the summer.
“You can sometimes get distracted by the outside noise and maybe for a little bit in the summer I was a bit,” Longstaff told the Newcastle website.
“It’s hard not to. Whenever you go anywhere, you see your face on the front of a newspaper and you turn the telly on, people are talking about you.
“And it’s not like they’re talking about little things, they’re talking about things that can change your life really.
“The expectation is half what I’ve done and it’s probably a good thing.
“It does just go to show I did impress people when I got my chance last year.
“So for me it’s about not listening to them and sticking to what I do.”
Longstaff also noted how he spoke to his Newcastle team-mate Matt Ritchie for advice on his situation, stating that he was helped kept grounded by the former Bournemouth midfielder.
“I speak to Matty Ritchie a lot, he’s someone I lean on in the squad,” he added.
“He tends to keep us grounded and he’s always there with good bits of advice.”
Newcastle are 14th in the league with their only win of the season so far coming against ‘big six’ side Tottenham in north London.