[MadAhab]

Tick saliva is meant to trick your body into not identifying it as a foreign object sucking your blood. So saliva, alpha-gal, and who knows what else is injected during the tick's feeding and that mixture is different than just eating food that when breaks down in digestion is turned into alpha gal.

It originates in a different place of your body (not from your gut) and has different components.

That's about the simplest I can explain the difference.