That’s the issue with vegetarianism. It’s not really about “the animals”, it’s about things that happen to resemble human beings. The more similar to a human, the more “sentience” it has. Isn’t that an odd coincidence? Or perhaps plants are just as sentient as humans but are a different form of life too distant from humans for us to empathize with.
The whole thing is a massive exercise in human myopia.
The burden of proof is on you. Humans are animals. We have evolution linking us together at a more-recent junction than we do when compared to plants. Humans and animals have brains; brains is the seat of sentience.
Finally; even if you are right that plants are sentient, are you then claiming that there is no difference in the amount of sentience between humans, bees, and plants? If so, should we be indifferent whether I kill you or burn a dandelion?
But even if it were just about not wanting to kill things that resemble us--it still doesn't have to be a false elevation of human sentience.
If there are fungi that make decisions, I'd expect them to look out for their fungus-buddies more than they look out for me. If Jupiter's red spot can be asked, I'd expect that it cares more for the weird hexagon on the poles of Saturn than anything going on on earth. Seeking kinship with similar things and being indifferent to alien things is common in biology, and it gets along just fine without sentience in the mix.
I think vegetarianism makes a ton of sense from an environmental and ecological point of view, but this has nothing to do with the moral one.