Whenever creating a custom ideoligion, it seems that all ideograms are available for selection, regardless of the origin of the ideogram or the origin of the ideoligion. It seems that ideograms should either all be available, or the text "unlocked by..." should be removed from the tooltip. Frankly, in my opinion, there isn't enough variety in ideograms, especially considering that these are just geometric symbols and any tradition could adopt any random geometric pattern. I vote that all ideograms remain available and the tooltip text simply get fixed.
To recreate:
1) Start a new colony
2) Create a custom Ideoligion
3) Select any origin
4) Add Ideogram Building
5) Edit the building. All ideograms are available for selection, regardless of current origin, even though the tooltip for some ideograms says "unlocked by <origin>".
Thanks for the bug report. When making a custom ideology you are allowed to create your own custom ideogram to. When it is telling you that something is 'unlocked by', what it is doing is telling you that that is its source. I can put in a suggestion that that be edited for clarity, it is intended for you to be able to select any ideogram. Sound good?
The wording "unlocked by x" is just misleading, since there is no actual "unlock" mechanic involved. How I understood you it's more like "suggested for x/typically picked for x". You can take Buddhism as your only style and then choose an ideogram that says "unlocked by Christian" without actually having Christian as a style. If there is no unlocking mechanic in place and this is by design, then the wording is the only problem.