That's no proof, there is no evidence linking the two metal pieces to the hypothesized trick.
Not obviously so, but remember: those metal pieces were found in a vacuum cleaner bag, among the broken glass that was dropped in front of Shizuki's room door. Kindaichi himself even said his fingerprints are bound to be on them.
So, to summarize:
Two thin, black metal pieces, the color of which match the room number as seen on the door, easily proven to have been in front of Shizuki's room door.
Said metal pieces having Shizuki's fingerprints on them.
Utsugi dying from a poisoned needle, which he came into contact with because he somehow mistook 1001 for 1004.
At that point, what other explanation can Shizuki give, exactly?