cross = angry!

so i've been tutoring this autistic boy for a few months now
it's a pretty easy job, all i do is read a book with him and get him to answer in complete sentences and do some reading comprehension.
easy money.
but sometimes working with these kids can be hard because their minds just don't work the way we do, and it's hard to explain things to them sometimes, they just don't get it.

today, we read a book about thomas the tank engine
and the word "cross" came up, so i asked him:
“do you know what cross means??”
he said: “cross the road!”
“yes good! and what else??”
“um…..cross the bridge…???”
“ok good…… but it also means something else.. something you feel… do you know?”
“i don’t know”
“ok. cross means angry”
“mm…cross means angry…” *nod nod*
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(we read more and find out that thomas is cross because he could not find the friends that were hiding)
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“ok so why was thomas cross?”
“cross means cross the road”
“no in this book cross means angry. so why was thomas cross?”
“because he was angry?”
“ok…….so why was he angry?”
“because……he could not cross the road……”
“………………………………………”

he just couldn't understand why cross means angry, and not cross the road.... or cross the bridge.....