Consider a situation where you called on Tom at his home. The following day, you can say to a mutual acquaintance
Tom was at home yesterday
In this context, it is neutral about where Tom is now. He could be still at home: he could be somewhere else.
Now suppose that, when you were at Tom's house, you asked him where he came from, and he replied
I am from London.
When you tell your mutual acquaintance, you say to him
Tom said he was from London. - reported speech - backshifted
Tom is from London - direct statement
You can use is because Tom is definitely still from London.
Similarly, when you interview your client, you might get these answers:
My name is Tom
I am 34 years old
I work at XYZ bank
My background is in IT
I work in accounts
When you are writing up your report a few months later, you would be obliged to say
His name is Tom - still true
He was 34 years old - at the time of the interview
He worked at XYZ bank - at the time of the interview
His background is in IT - still true
He worked in accounts - at the time of the interview
I am not suggesting that you should always switch between present and past like this: it is just an example that shows how you can express these ideas precisely if required.
If it's not necessary to be precise and you have multiple items of information, it's probably best to stick to whichever is the most common of present or past: the context will usually be enough to avoid misunderstanding.
If precision is important, it depends exactly what you mean by "from the IT field". If it means "His training is in IT", then it's still true, so you should use is. If it means "He is currently working in IT", you should use was.