This is wrong … Isa (AS) is denying ever teaching the people to worship him, he is not denying knowledge of the fact that they worship him. He is also appealing to the idea that they must have started worshiping him (AS) in his absence where he could not monitor them and tell them off.
You are totally misreading this verse in fact you are taking the impact of the meaning out of this verse … it is nothing to do with his (AS) knowledge on the matter …
It is to do with preserving the teachings of tawheed … Isa (AS) point blank says he never told them anything other than tawheed … whereas your version seems to be saying … “I dunno what they were doing” … this position takes the real impact out of what Isa (AS) is saying … which is that while he was watching the people HE MADE SURE THEY DID NOT DO SHIRK WITH HIM … while he was not with them HE COULDN’T MAKE SURE OF IT and that ALLAH ((SWT)) knows full well what is in his heart about what he portrayed to his people.