Precise modifies ideas. The videographer was amazed that Cobain not only had ideas but had brought them to a point that they were precise, ready to be shot, rather than vague ‘concepts’. Syntactically, precise is a secondary, object-oriented complement
We have the report ready to publish. = We have the report and it is ready to publish.
He had those ideas precise = He had those ideas and they were precise.
Did here is a “pro-“ form—a word that ‘stands for’, acts as a repetition of some other entity previously named (or, occasionally, about to be named). Just as he is a pronoun stands for the noun phrase somebody (which in turn stands for Kurt Cobain), did is a proverb standing for the verb phrase HAVE those ideas.
Constructions of this sort are not ordinary ellipsis: it is the sense of the verb, not its form, which is repeated, and the verb can take a different form to suit the syntax. So if we expand the reference we get
... having those ideas as precise as he had those ideas.
This sort of comparative construction is fairly common. You might say, for instance:
I am happy to find calculus as easy as I do (= as easy as I in fact find it)
This is roughly equivalent to “I am happy to find calculus so easy”, but it allows you to be a little more emphatic by ending your sentence with the assertion that you do find it easy.
In the same way, the videographer puts it this way because it allows him to emphasize that it wasn’t just how precise the ideas were that amazed him but the fact that Cobain, a songwriter, had such precise visual and cinematic ideas.