It looks like the candlestick recipe is tricking you by basically just putting bars centered at 0.5:1:nrow(ta) and then overwriting the xticks with the dates. You can do:
plot!(0.5:1:20.5, values(ta.Open))
I think ideally they would just use the actual Dates as x locations, but there might be reasons I’m unaware of why they had to do it this way. Maybe worth filing an issue?