Should have given the goal as he is clearly onside (assuming the line is correct). Offside should never be too close to call, you are either on or off, or level in which case you are on.
It does depend on the quality of the technology available though.
I have seen some clips from the MLS in America where they seemingly only have the camera angles (sometimes not even fully in line) and don't have any lines to impose, etc. and there have been times the VAR has said something along the lines of 'we can't tell' and gone with the on-field decision.
I heard the other week that in the Premier League they will be using a 2D system rather than the 3D system that was used at the World Cup so there is some room for potential inaccuracy in offside VAR decisions.