It's a strange one! More digging is required!!Well that starts to build a case...
Played North Melbourne 1907
1908 April 18 - RFC practice match 'T Johnson' (halfback, Lancefield and Carlton)
Transferred to Richmond on 29 April 1908
Played 9 May 1908 with RFC (back pocket)
Transferred to Nth Melbourne 5 June 1908 (or one or two days earlier)
Played 6 June 1908, and 13 June 1908 with Nth Melbourne as a half back.
If that is him, then it is improbable that he played with Richmond on the same date 13 June 1908 (I'm assuming the Herald report is from that afternoon's match)
Meaning the 'Johnstone' listed as forward pocket for RFC 13 June 1908 (Rd 8) is not him, but an entirely new player.
To add fuel to this, the 1908 Annual Report lists W Johnson under the PLAYERS heading. It does also list a J Green , who isn't credited with a senior game yet and appears to be in Rd 11, 13, and Rd 15 squads (and maybe more) that year.
Hopefully the Richmond Guardian, or Richmond Australian sheds some light on it.