The England winger put Liverpool transfer rumours behind him to commit to the Magpies.
Howe said: "It was a difficult summer for him, there's no doubt about that. It was a difficult summer for a lot of the players because, through no fault of their own, they are reading headlines on their futures which can be destabilising.
"Anthony had the Euros which was a brilliant experience for him - maybe didn't play as much as he wanted - so there was a frustration there - but then he's thrust back into the action here and he'd hardly had any training and hadn't played in the Euros.
"There was a lot of psychological aspect to deal with and I think he's handled it really well I think this move by him just ends any other thought other than being at his best for us which is his priority and always has been his priority but hopefully it accelerates that."
Howe was also asked ahead of Sunday's trip to Chelsea about news that contract talks with Alexander Isak have been called off.
He added, "Regarding the contracts, I'm not necessarily involved in those discussions day-to-day, I will hear bits and pieces.
"With Alex, he's got a long contract anyway and we have to be careful regarding our spending due to PSR.
"It's not a clear-cut situation, we of course love him and are desperate from him to stay at Newcastle for many years and score loads of goals for us. But I don't see a short-term issue with his contract."