Translation:He does not eat pork, because he is vegetarian.
I don't find it ambiguos at all. I think it is pretty objective and understandable. The thing is that the english language has the auxiliary do. As an auxiliary verb do is used with a main verb when forming interrogative or negative sentences, or for adding emphasis. We don't use the auxiliary do when it comes to the verb "to be". That is why we translate "li ne estas" to "He is not" and not the other way around, while all the other verbs will be tranlated to "does not".
sxi ne trinkas - she does not drink
ili ne dormas - they do not sleep