Building Christian units/buildings with Almohads

According to some of the unit guides, some Christian units (including knights!?) are available to the Almos if they have the requisite buildings.

Does that mean I should work extra-hard to capture / bribe built-up Christian lands so I can build heavy knights? Or was the unit guide incorrect?

btw, how do I know what "era" I'm in? Is there an obvious or obscure popup, or do you just have to know what year the middle / late era starts?

The guide is incorrect, when you as a muslim capture a province with christian buildings, such as churches and chapels they'll automatically be burned down ie. pillaged, So you cannot build christian heavy knights as a muslim, this ofcourse works vice-versa.
About the time period, there is no popup and the dates are 1205 for high and 1314 for late, although I'm not sure about the latter...