Lemon took the more measured of the two options, knowing that if Zischke continued his good form then he could have six rides anyway. Otherwise, Lemon was looking at Zischke being forced to take 7 rides, and Cairns 4, with Blödorn having to take the R/R in 12 (with your benefit of hindsight, apart from an excellent gate & go in Heat 5, Blödorn's only other point was ahead of Killeen - and he would have faced Etheridge in 12).
It's all about scenarios and options - I thought before the meeting that Lemon had made the correct choice to use a guest, and it was proven to be fairly successful.