Wow.
I'm very surprised that so prominent an allergist would downplay sesame, of all things.
Does your child have a very specific
reaction history with sesame?? Or is it that s/he skin/blood tests as allergic?
If it's the latter, I'd be asking for a food challenge if my child were >~4yo. Sesame is one that, like peanut and treenuts, seems to be pretty potent as an allergen.
The threshold dose required for people who are really allergic is VERY small. Certainly way less than a sesame seed or two.
It does sound like the kind of advice that might be given to parents who had a child with an elevated RAST but no specific reaction history, however. We were in that camp for many years until we finally challenged sesame informally (we live near a hospital, though, and have a LOT of experience, so this is what our allergist recommended we try-- DD had previously eaten sesame in hummus and other foods before testing as allergic to it).
We never went to any real lengths to avoid traces, basically following the same sort of advice you seem to have been given.
I know several members of this community who HAVE had reactions to foods when using that kind of strategy, though, I'm afraid to say. So it doesn't seem to be a very good idea for someone who is actually allergic.