Ahmed Hassan was a shy young man who chatted to college mates about Godzilla, Trainspotting and his love of horror films, a court heard.
But despite his success in photography and creative media at Brooklands College in Weybridge, he led a secretive life, jurors at the Old Bailey were told.
If he had any close friends, they remained a mystery to college classmates and it was "impossible to know about his life", the court heard.
Reece Allingham worked with the 18-year-old Iraqi asylum-seeker on a "superheroes" film project which was marked with "distinction".
He said in a statement that Hassan was "quite shy" but they would joke about "silly stuff" like Godzilla, and fake blood and watched Trainspotting together.
Following the Manchester Arena bombing last year, he said Hassan told him it was "sad people had been killed and hurt".
The only "odd" thing he noticed about the horror film fanatic was one occasion when he found him sitting in a dark room on his own at college.
Lecturer Sue Pattinson said in a statement that Hassan was "traumatised, on edge and not very trusting" and spoke very little English when he first went to Brooklands.
Moving in with foster parents Ron and Penny Jones "invigorated" him, she said.
Ms Pattinson said he was not a chatty boy, but he would talk about his love of sport and football rather than political or religious issues.
Yayha Farroukh got to know Hassan because they were both alone in Britain and Arabic speakers.
He helped Hassan find a foster home with the Jones family, but soon discovered they had little in common, he said.
In a statement read to court, he said Hassan had told him he came to Britain from Iraq via Turkey, Italy and France.
He wanted to be "safe" and told him he had been detained by terrorists for one and a half months.
Mr Farroukh said Mr and Mrs Jones were "extremely kind people" who had put him up before Hassan took over his room.
He said: "I thought it would be nice for Ahmed. When I moved out of Penny and Ron's I stayed in touch with them and have been close to them ever since.
"I have retained contact with Ahmed more out of necessity than choice as we see each other at college and when I see Penny and Ron.
"Although we initially had things in common such as language and lack of family in the UK, I would not describe him as a close friend.
"We are very different people with very different outlooks on life. Ahmed has never really spoken to me about his friends, although he is constantly on the phone to them.
"If he was away for four or five days, he would be staying with them. Ahmed has his own life.
"It was impossible for anybody to know about his life because he was so private. The only people I ever heard him speak to were his uncle and Penny."
Mr Farroukh visited the Jones's home in Sunbury, Surrey, on September 3 last year.
He found Hassan's bedroom door was broken and had the word "bored" scrawled over it.
Hassan explained to him he was "tired and bored" at home, while his foster parents were on holiday in Blackpool.
The witness also saw two vases in the room which Hassan said he "needed", but did not explain why.
He told authorities: "I do not know what bomb-making material looks like so I would not have recognised it if I had seen it at Ahmed's house."
Hassan has denied attempted murder and using the chemical compound TATP to cause an explosion that was likely to endanger life.