I doubt Matt Nathanson would make a big deal out of it. That's just one freaking line. He could've sued her when he found out, but he didn't. Or she could do some sort of an agreement with him like putting his name on credits, if the song released as a single.
He spoke about it again recently.
Quote:
TORONTO — Singer-songwriter Matt Nathanson said Friday he learned a valuable lesson last year about the power of Taylor Swift fans.
The 40-year-old musician went on Twitter to call Swift “a thief” after lyrics from his 2003 single “I Saw” showed up on her song “All Too Well.” — sparking a barrage of angry and defensive tweets.
“They swarmed,” Nathanson said of Swift’s fans, “I got 11-year-olds beating me down. They were vicious.”
He deleted the tweet but followed up with one that read: “So far, my favorite thing about today is the wave of @taylorswift13 fans calling me a p**** on twitter for writing ‘i saw’ in 2003.”
Appearing on Global’s The Morning Show, Nathanson said he was taken aback by the reaction.
“I’ve never seen anything like it in my life.”
The “Come On Get Higher” singer insisted he wasn’t even completely angry at Swift.
“I was 90 per cent flattered and 10 per cent ‘I worked hard on that line,’” he explained. “It’s all good.”
Im sure he's never written a line in a song that sounded like someone else's song. It was his calling her a thief that was unprofessional. He could've brought it up using a better choice of words
He seemed a bit bitter though 
They should finish it. The face she pulls. 
TOMG the original >>>>> 90% of her discography