Wide = across the body of the whale from side fin to side fin
Long = the length of the body of the whale, from mouth to tail
So the sentence you came across tells me that the whale was very wide, but doesn´t tell me anything about how long it was, so your #2 wouldn´t work in this sense. Unless the writer used the wrong term, but one can´t necessarily assume that.
And in answer to your final question, both #1 and #2 work in English, depending on what you want to say.
Generally speaking, we think of width as being shorter than length*. So a 10-metre wide whale would be expected to have a length of more than 10 metres - and given the shape of a whale, maybe 5 times as long. Which would make it 50 metres long. That seems unlikely in this context: I'd guess the whale is actually 10 metres from nose to tail - which we would describe as its length.
* That is a GREAT generalisation, but for this example it may be enough. See other threads / dictionary for more description.
The sentence was from the newspaper this morning and it's got a picure of the whale above it. Yes, the whale seems to be about 10 metres from nose to tail, and the caption that goes with the picure has that sentence in it.