No. It only means that Google forces App developers to set it to 26+ if they want to upload it to the store.
Setting it to 23+ causes Android to use new logic on newer devices (older use the old level) like "no app is allowed to store anything unless you ask the user via runtime permissions".
That is interesting. I only ever write apps for my "personal consumption" so if the restriction is only enforced on a upload to Google Play I will have nothing to change. Fingers crossed!
When you think about it seems likely that the SDK level will be checked for on upload to Google play. Where else could they do it? It makes a lot of difference to me. I wonder how many other people are like me and only ever develop for themselves. Because of the uncertainty I don't whether to start work on apps or wait and hope that it won't be necessary!