Yes, I admit it is a bit confusing in this chart (it is old and will be updated in future):

Delta = spread = (R-MA)

Thresholds (green "band") = Entry and Exit thresholds multiplied by StdDev

From the mathematical point of view it is equivalent here to work with Z-Score and constant threshold or with Delta (spread) and thresholds multiplied by StdDev...it is just a different graphical representation of the problem.

So yes, the trade was opened because the spread crossed the -2 deviation point. That's mathematically the same, as if the Z-Score crossed the -2 line.

The chart for ratio model backtests will be updated in future also to show the Z-Score too (same way as the chart for Residual model, which already shows the Z-Score graph).