Westley, whose tumultuous 13-month spell as North End manager ended when he was sacked in February, endured a grim return to Deepdale on Saturday as his Boro team were beaten 3-0.
Paul Huntington, Scott Laird, against his former club, and Kevin Davies were all on the scoresheet for the hosts.
But Westley claimed much of the success Simon Grayson's side have enjoyed this season was down to the work he did last year.
"It was always going to be a really difficult afternoon," said Westley. "It was a shame to give away the goal that we did, it was a moment of defensive indiscipline from a set piece and that isn't normally a feature of my sides.
"I believe I bought good players for Preston North End and those lads, now that they're fit and playing, are showing the types of qualities that we know they've got. They are all lads that can make a difference at the top end of this league.
"I never get a particularly good reception at an away ground. I would have thought they would have been quite gracious towards me here because I think I did a lot of good work for this football club.
"Last year was always going to be difficult, especially when you get big injuries like we did. The club wasn't patient, they've brought someone else in, he's added four internationals and they're going strong - I would have expected it to happen."