Question

how can you say that michael and his father had a passion for computer games

Answer 1

Yes, Michael father was nutty about computers and as Michael was his son he was too interested in tech gizmos. 

He made his home loft a powerbase and used to play games there. 
The presence of great computer parts as given in the fiction showed that he was really passionate for computer and computer games

Answer 2

Michael and his father had a passion for computer games.
They had a Pentium 150MHz, hard disk, 16 speed CD Rom with speakers,printer,modem and scanner.

They had a collection of computer games which the narrator always played.
Michael's father couldn't resist any new gadgets that came  in market.The evidence that they bought latest psycho-drive games with virtual reality visor indicates that they both had a deep passion for computer games.

Michael's father had also converted the loft into Powerbase for his son to play there.