Angulo was a veteran at Los Che when Mata was given his opportunity to shine after arriving from Real Madrid Castilla in 2007.
The Spaniard spent four years at the Mestalla before Chelsea came calling in 2011.
It was at Stamford Bridge where the attacking midfielder made a name for himself around Europe after helping the Blues win the 2011/12 Champions League final.
When asked about Mata's career since, Angulo said the 32-year-old had fulfilled his potential in England, while praising his personality off the field.
"He's a player that can play in different positions, which has made him an even better player over the years. I believe that he has achieved his potential in England.
"He left Spain quite young, where he was shining in La Liga. The English could see his great potential and that he was different kind of player too.
"With his quality and character, he is a player that could play in any team. He's a player that left his mark at Valencia CF and was much loved here for his character and style and his whole way of being as a professional footballer.
"He is 'buena gente.' A really good person and a really great footballer too."
Mata signed a contract with United last summer to 2021.