Darjeeling, black tea or oolong?

Short answer: it can be anything

Darjeeling is a place in India just like Yunnan is a place in China.
Both produce a variety of tea variations, but they are known widely for specific types.
Darjeeling is generally refered to as a black tea; but it’s possible that you had an oolong, a black, or something from another dimension.

Yes, I know that there are greens, oolongs and also white darjeeling teas, but comparing the darjeeling black teas with let’s say assam or chinese blacks the leaves seems less oxidized and zome of them look green.

there is a green darjeeling. maybe they just got mixed up :)

First flush darjeelings are less oxidized, so they retain more of the floral, green, spring-like flavours. So the leaves look greener and respond best to cooler-than-boiling water.
http://happyearthtea.com/blogs/blog/7784655-why-is-darjeeling-first-flush-so-green-in-appearance
http://hojotea.com/en/posts-29/
http://www.teatulia.com/tea-101/what-is-first-flush.htm

Technically its an oolong going by Chinese standards, but its not a Chinese tea, so it’s whatever the producers label it as…

So, for what you say, first flush darjeeling can be considered ‘oolongs’ if we view it from a Chinese classification point of view.

Yes, because oolong in the Chinese system means between 20-80 percent oxidation. Iirc, mot Darjeeling falls around 70 percent.

By looks, taste, and processing, Darjeeling blacks are equivalent to Chinese oolongs. Nilgiri and Assam blacks are…well, black; with Assam’s being a stronger black.