First of all there is a thing the man was on the ice block trap died but he was not eric matthews here are some reasons
1 Eric matthews character is very coleric and this is shown in saw 2 thing that does not happen on saw 4 he didnt talked a lot and shouted.
2 the trap was created by john and hoffman and if we remember hoffman doesnt kill people when hi is with john and if we remember in saw 2 kramer remembers eric why he was there because of the last words he said to his son daniel matthews but also jigsaw knows eric tried to call daniel because he was regretful and as he said to hoffman everyone deserves a second oportunity.
3simple facts eric matthews was dissapear for more than 6 month and when he dissapeared he broke his foot and a foot takes maximum 4 months in heal so there is something wrong.
4 when we see eric matthews he has blood on the face and that means that it has too be an event that we did not see in the movie and this is were john kramer put a similar person from his games .
5 john kramer did what i put on number 4 to show daniel rigg what he wanted and he didnt want to put eric because he knew eric was regretfull.