This is pretty much cannon. But I think there is another layer to it.

The Devil of All Earth gave Ymir Fritz this power. Usually things like this come with heavy strings that cause the "gift" malfunction maliciously.

One of those heavy strings is the fact that Mindless titans have two basic rules that guide thier existance as far as eating humans goes:

(1) This is thier base state, they only react strongly and predictably to stimuli when that stimuli is a human pressence. Titans don't generally do anything else. They only want to eat humans and this is regardless of knowing or not knowing the human may turn them back into a normal person. That is irrelevant because they do not have the capacity to think that far. Titans do occasionally show a memory of thier former self, but this seems to be in all cases fleeting and not representative of the titan's current mindset. Its a phantom reaction, false hope. The titan will always obey its primary reason for being. It is a mindless tool of war formed from a living human.

The (2)nd rule is that they will become titan shifters if they are either intentionally fed a human or accidentally happen across one. But they don't actually know this is a possibility because again, they are mindless husks.

These strings also play on one another because they can interact in unplanned ways. Ymir (present) eating Marcel for example. In this case an unintended sacrifice is made and Ymir gets her life back. From the panels that describe her journey from human to titan and back give no indidcation that mindless Ymir had any inkling that eating any human would turn her back. She only realized what must have happened when she realized Reiner and Bert were also shifters.

Also in the case of Eren Jaeger he had no idea eating Grisha would make him a shifter. That was just his ground state as a titan, he needed to eat Grisha because that is the only thing titans know how to do.