I know I've read the same. New growth in small quantities seems OK, (
https://homeguides.sfgate.com/lathyrus-latifolius-edible-104906.html) but with many plants like this, I suspect there may be many differences in tolerances between people.
For example, there are many foods with Oxalic acid in them. (rhubarb, sorrel etc). We know that too much oxalic acid is a bad thing, but little bits are OK. But I have a tendency to gouty arthritis, so the amount that I would risk eating, is considerably less than what others might see no ill effects from eating.
The chemical they're concerned about in Lathyrus latifolius is oxalyldiaminopropionic acid and one of it's affects is on breathing. That suggests that I- physically small lungs - and a friend of mine - asthma -
should probably pass on eating this veggie. However, I have a different friend who freaked when I suggested someone have licorice tea to help her cold as there's a chemical in licorice tea that can increase blood pressure. I happen to have low blood pressure, so if I'm stuffed up, I'm happy to have a mug of it.
When we should pick, how we should prepare, and when we should take a pass on uncommon foods is a complicated subject. Grocery stores don't want people to have to do that sort of research, but a few hundred years ago, that was one benefit of community living and what made elders so important as they were the holders of that sort of information!
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